"Whoo! A mechanic could retire working on that thing!" So said the head of maintenance where I was a Flight Instructor. You see, a doctor moved to town. He brought with him a Cessna P337 Skymaster. The deciphered meaning? A pressurized multi-engined plane crammed into the space of a single engine plane.
The concept was simple. Center-line thrust (engines mounted in the same thrust line) meant that in case of engine failure, the plane would fly straight ahead and huge control changes would not be required to maintain control. Sounds great. Cessna decided to make a plane they could market as safer to fly than other piston twin engined planes. Then, they loaded it up like Nissan did to the 240z and Porsche did to the 911.
The first plane was the model 336. Fixed gear, two seats, with two 195 hp engines and could carry 1,000 pounds of people and bags with full tanks of gas. this was 300 pounds more than a nice 182 Cessna could handle and only 5 knots faster. Easy to control. Relatively easy to fix.
Then They gave it 210 hp engines and retractable gear. Then, pressurization and turbocharged engines. I don't know how they got all of the plumbing in there. Just like the nimble little 240z and 911 evolved into more GT heavyweight speedsters, the 337 became stuffed to the gills with more stuff without making it larger. It was a fun plane that cruised swiftly and at high altitude but you did have to maintain an overstuffed GT at this point.
So, designing more into a design that did not have any of this planned to begin with, left things hard to reach and that's the problem. The design afforded the ability to pay a mechanic lots and lots of money over time to fix all of the little things that are hard to reach. Want a new boat or to get closer to retirement? find an airport with a few P337's and get to work.