Looks good - and is true that few of these did not have vinyl roofs. https://detroit.craigslist.org/mcb/cto/d/port-huron-1974-buick-electra-225/6827420756.html
Are we sure that is not a repaint..!? That does not look like a 70’s color.. and doesn’t look right with that interior. Looking at the plastic interior trim.. I’m guessing this was originally a yellow car!? Also the plastic bumper trim moldings are missing off the front and rear bumpers.
I think it's factory Gold Mist Poly. I'd say black interior would be the "recommended" interior trim when someone ordered this car new. I'd say Saddle is the next best "acceptable " interior trim. You definitely would not want the other available interior trims: blue, green, or red. I agree, not putting a 455 back in really hurts the appeal.
If it had to be Chevy power, then drop in a Bigblock in a full-sized car. What he did looks cool. But, like you write, it marginalizes his ability to get rid of it I thought, vinyl roofs were standard, on those. If they were, this one doesn't look bad, without it. In fact, it looks more like a bachelor's car, without vinyl. If I had no choice, when buying one new, I'm sure that I'd peel the top
