I knew about the early Rivs, and the Boat-tails... but the 2nd generation didn't really strike much of a chord with me... but in a way, it is the sleekest and coolest.
66-67 Buick Riviera.
I am imagining this as a sweet resto-mod, with this car's gorgeous, handsome lines, hidden headlights, and pillar less side-windows, rear fender arch, and fastback roofline... so much good material here... and it is still RWD, unlike the Toronado and Eldorado platform-mate e-body coupes.
7.0 Liter LS7 crate engine (darn close to the 430 Buick V8's displacement), with a 6-speed automatic, and a limited slip disk brake heavy duty rear axle, with upgraded front suspension and disc brakes also. Maybe airbag suspension, since it is a luxury car, rather than a performance car.
Clean bodywork with modest chrome left on the body. Shaved door handles with RFID smart-key locks and poppers, and a start button, like a modern luxury car. One touch power windows, retained accessory power. It would be great with an electronic push-button automatic gear selector, and then shift paddles behind the steering wheel, on an aftermarket steering column. Some nice luxurious premium leather recaro front seats.
LED lighting replacing incandescent bulbs throughout, (including tail lights and JWSpeaker LED headlights) etc... The turn signals on the inside of the front fenders would be great with white and amber LED switchbacks, for running lights and turn signals.
A nice set of staggered fitment wheels and tires... probably something like 17" front, and wider 18" at the back, with some tires that actually have some sidewall, rather than going too tall with 20" or more.
Something with old school looks and fine lines, but thoroughly modernized mechanicals and amenities.