Ahhh, dammit, my weakness: cars that look like race car extras from any Dukes of Hazzard episode! Inappropriate vehicles give the semi-stock car look encourages violent driving in my book. It’s a delinquent’s car, the set of wheels that you don’t give one flying fat one about MPGs or whether or not the HOA is about to send you a very strongly worded letter about “that contraption” that has striped every last ounce of asphalt in sight. It’s the car that is the equivalent of the devil on your shoulder, poking you in the neck with the pitchfork, urging you to go full-on hoon and to not stop until you need new tires. I love ’em, and this 1971 Buick Riviera just throws jet fuel on that tire fire. 
Drawn up by Jerry Hirshberg with Bill Mitchell close by, the boat-tailed third generation Riviera wasn’t quite the success that GM was hoping for. Was it too radically styled for the tastes of the day? Probably. But for every negative comment I’ve ever heard about a boat-tail Rivi, there’s plenty of takers. At least you won’t have to worry about blending in with the crowd…unless a Bugatti pulls in or Gal Gadot shows up and starts signing autographs, your Riviera is going to have eyes on it at all times. 
So, here’s the dilemma: right now, the Riviera is a roller. You can put the original Buick 455 back into the car and enjoy a bit of fun from back in the day. You can build up the old Buick and have enough torque to make the big E-body dance around like it was a small-block swapped Vega. Or, you now have the opportunity to repower the car. With that comes a lot of temptation…would you give in?
Big cars need big motors – if I got that one, the 455 is going right back in after some basic maintenance.
Freshen up the 455 and put it back in.
Without a doubt the 455 freshened up with a very mild cam and an overdrive trans behind it. Maybe a TBI setup under there for the added tunability from within your new road sofa.
This 110%. That’s how I would do it too.
One of the reasons the Boattails didn’t do as well is they were supposed to be on the A-special chassis (Monte Carlo/Grand Prix) but got pushed upsize to the E-body (LeSabre/Impala) and the size increase didn’t work as cleanly as people wanted it to.
I’ve always wanted to try and take a Grand Prix and a 71 Riviera and slice and dice them together to get the original scale back
I’d be interested in seeing a rendering of what that might look like. Supposedly one of the Buick stylists complained that the up-sizing meant “We started off going for a speedboat and ended up with a tugboat”.
A nice 350 would get the job done!