Here's an alternate world scenario: The Ford Flathead V8 doesn't catch on in its first three years, but the Lincoln-Zephyr V12 is loved by all, and is produced for many years. Let's do some speculation:
Criticized as being too heavy and costly for a pedestrian engine, but too weak and simple for a luxury car, the Flathead never starts the American V8 trend. But after seeing great success with the Lincoln-Zephyr V12, Edsel Ford's Lincoln-Zephyr brand continues until Lincoln is consolidated into the single Ford Luxury brand: Zephyr Automobiles.
Cadillac, seeing this, follows suit with their 368 V12, which is a massive success also. Buick begins research on their own V12 to compete.
Using exclusively the Zephyr V12, the Zephyr brand is a huge success as a cheap luxury brand, providing no need for Mercury to be formed. Edsel doesn't die in the 40s, and he manages the company expertly, so Henry Ford Sr. never takes over and dies peacefully.
The young, spunky Edsel will carry the company well into the 70s. Other low-end V8 Lincolns do not get the V12, and pull down sales. and the Lincoln Brand is eventually consolidated into one luxury name: Zephyr Automobiles, which produce small-displacement luxury V12s. Cadillac has continued its V12 line, and now it's the only engine they produce.
Buick doesn't make a Nailhead V8, they make a Nailhead V12 at around 350ci. A horsepower war starts in the 50s between the two V12s, with the smaller (250 ci~) Zephyr V12 not able to be made much larger without sacrificing reliability. Ford resorts to a (crude) supercharger to power their luxury cars in the 50s, getting the idea from Deusenberg, and setting some top speed records in their ultra-exclusive 350HP Zephyr Continental. Buick, occupying a lower-end market, stays naturally aspirated, and shares its engine with Chevy to fill the gap.
^ This is what the engine bay of most luxury cars looked like.
Pontiac never gets a V8 and as its aging I6 engines are phased out, it is killed very early.
With the massive Cadillac V12 out there, the Continental can't keep using the smaller Zephyr V12, so they develop a big-block V12 for the top-of-the line Zephyr Continental. It stays supercharged, and now pushes 450HP out of 300 c.i., and 320 HP out of the N/A version.
Here's where it gets interesting: Because of a lack of demands for V8s, and the popularity of cheap luxury V12s, Chevrolet never designs the small-block engine. Following World War 2, most non-economy US engines are smaller (200-300 ci) high-efficiency V12s, and most economy engines are 100-200 c.i. I6s. The biggest implication is that R&D learns how to make an engine spin faster and higher with less weight, and ignores things like fuel injection and turbos to get more efficient power, instead focusing on timing, RPMs, and airflow.
The new Corvette is released with an I6, but instead of it being an anemic left-over from the 30s, it's a new I6 developed from Buick's Nailhead V12. Suddenly, the market is hit with a 200 CI I6 that weighs basically nothing and had around ~200HP. The car is a massive success and starts a trend of I6 tuning. People start gutting old luxury V12s for valves, cams, and other parts that will fit their I6 'economy' cars and start hotrodding.
Jaguar sells decently, but sort of becomes an also-ran since their lineup is basically identical to other cars. They lack the reliability of most sedans however, but make up for it in looks.
Ford needs to keep up, so they raise the redline of their N/A V12 line to 6500rpm and squeeze 350 HP out of a N/A 300ci V12, beginning a specific power war at the mid-range automobile market. In pursuit of specific power, Ford plays around with Fuel Injection, but FI systems are relatively crude as of now, and Buick is way ahead of them on that.
The abundance of powerful domestic V12s makes cars like the E-Type and the Ferrari 250 seem lightweight imitations of the original Corvette or stripped down non-luxury versions of the Zephyr Continental, and they don't sell well in America at all, making Ferrari's financial scenario much worse. The GT40 features a 427ci V12, decimating them at Le Mans. Ferrari goes bankrupt and is ultimately bought by Ford, much to Enzo's distaste.
The Dodge Bros. are sold to Chrysler, who releases the original 300 as an 300 c.i. I6, not a B-block V8. The large-displacement I6 makes them drag-racing dreams for mechanics. They dominate Nascar with a higher-torque engine. Hudson gets a much larger dodge-desgined 400 c.i. I6 to play with, and they occupy the lower-end sports car market.
The Ford Mustang is released with a lightweight I6 and no V8. Caroll Shelby gets the bright idea to stuff a Ford V12 (from the GT40, right?) in it, and the Shelby Mustang, rather than being a tuned engine, is an entirely new beast. You can't get a V12 Mustang unless its a Shelby. In 1970, the Shelby Mustang features a Lincoln-designed 427 V12 that has ~450 HP. This gives them something to blow the 400 c.i. Chrysler/Hudson/Chrysler I6 out of the water.
The Camaro sells as a cheaper, more economic I6. Not wanting to sell their Caddy or Buick V12 in a Chevrolet, it never gets a V12, so the Shelby Mustang remains much faster, and the high-end Camaro competes with the low-end Mustang.
Ford, getting the idea from Shelby, puts their V12 into a Mustang, but sells it... as a Ferrari. The new Ferrari "America" is a V12 muscle car with good handling. Cadillac releases The Zephyr-Ford-Ferrari triumvirate dominates international racing, making sporty cars. The Mustang quickly becomes a cheaper alternative to a Ferrari, and it competes directly with the Corvette. The Camaro is a cheaper alternative to the Dodge-Chrysler-Hudson I6 muscle cars, and are primarily used for drag racing and Nascar, with a big-displacement I6 is better than a V12.
Ferrari begins to sell a mid-engined car based on the Zephyr as well.
Dodge now competes with Chevrolet for the compact sedan and small muscle car market. Buick offers pricier options to both and competes directly with Ford and Hudson, Ford with some V12s, Hudson with superchargers, and Buick with Fuel Injection. Ferrari is kept docile and out of most racing, and Ford guts their cars for suspension technology (which mostly goes into the 67+ mustang, which is now similar in design to a Ferrari 250), and enters Formula 1 with their Cosworth DFV V12 under the Ferrari Name. Zephyr drops out of Nascar, but does get the top-speed record (190mph) for 1968 in a road-going version of the GT40.
Chevrolet introduces a Camaro Z/28 with a supercharged I6. It lacks the handling and sporty, high-revving nature of the Mustang, but it has the top speed and torque to do well in Nascar and is now not really a Mustang competitor, but goes head-to-head with the now 3rd gen Hudson Hornet's Supercharged I6.
So when the Fuel Crisis hits, we have:
Ford (small I6s), making sedans and the Mustang, Shelby Mustang has a Zephyr V12. Some sedans have optional 200ci V12s. The Mustang has IRS and is similar to the Ferrari 250.
Zephyr (large V12s) making the Continental and some Luxury sedans. Top-of-the-line cars (Continental) are high-speed (160mph+) and supercharged. They now have a road-going version of the GT40 with a massive 427 V12, and it holds the top speed record.
Ferrari (small V12s) making beautiful high-rev Muscle Cars, but not selling at higher prices than Zephyr. They sell the "America", a 300ci Zephyr V12 Mustang, and a smaller 2 seater with a 200ci Ford V12.
Dodge (large I6s) making cheap econoboxes, most cars are not luxurious at all, but they're great among drag racers who fit Hudson parts onto them.
Chrysler (large I6s) making luxury versions of those econoboxes. They sell the 300, a rebadged Hudson Hornet with more luxury components, and some luxury sedans. They compete directly with Ford, and their top-level cars have 400ci big-block I6s.
Hudson (small I6s) making high performance versions of the econoboxes. Dominates nascar through the 60s. The Hudson Hornet R/T has a 400ci Supercharged I6, and is the only car that competes with the Zephyr Continental for HP, but doesn't have the luxury or reliability.
Chevrolet (small I6s) making the Camaro and some sedans, a cheaper, smaller alternative to the Hudson and Ford cars. The Camaro Z/28 competes with the base model Hudson Hornet, and both are much heavier and worse at cornering than the Mustang.
Cadillac (Large V12s) being the only competitors (outside of Rolls Royce) to Zephyr. They make larger (400+ci) N/A V12 engines, but can't match the same top speeds as the supercharged Zephyrs. Interiors are a little nicer, and the ride is better.
Buick (small V12s) being an entry-level luxury sports car company. They make 2 door versions of the Chevrolets with a small, high-revving FI V12. No true 'sports' cars, but they have the most Fuel Injected models, something that Ferrari, Ford, or Dodge haven't yet caught on to. Best specific power, and some models have good handling.
Now, what do you think would happen in 1973?