Question on rear wheel sizes

I have always loved the looks of those 2-dr cars. and I have always wanted one. But If I had one, the absolute first thing I would do is install tubs big enough to accept at least 275s on at least 10s, 295s on 11s would be better.
and then a narrowed rear end,
and for sure, slapper bars,
and then specialty shocks.
Now I'm ready for a hot 318; or a stockish 360 would be better. But best would be a small-cammed Hi-compression 340; man that thing would fly.

It's either that or re-profile the wheel opening and install some tasteful flares, matching fronts and rears. Or maybe a wide-body.

Which is the main reason I don't have one of those cars,
cuz that type of work is beyond my skill-level, and to pay someone around here, I'd have to mortgage my house. and at age almost 71 and retired, that will never happen.

So, on a budget as I am, I would do as Mike said, but go a little further. I'd yank the rear-end right outta there, roll the new wheels in there, center them, measure between the mounting flanges, at ZERO clearance to the inner tubs, and moving the springs if I have to. Then I would have a professional narrow my 8.75, to that spec. When I get it back, it will be about 3/4 inch too narrow. This will allow you to space the rearend to one side or the other, with large machine-washers, to match it's most likely off-center factory installation. When done, you simply order the proper wheel-spacers. Nowadays any machine-shop with a CNC plasma cutter can whip those out in minutes.
If your wheel studs get too short, I'd plan ahead for shank nuts. But if your style of wheel, that you really really want to run, does not accept those, then you may need to get longer studs. no big deal.
For me, that would be sorta my dream car. I would dress it up with a tan-leather interior, a 4speed auto and minimum 3.91s in the back. and it would be wearing the bigger spindles cuz I broke two of the niners already.
yada-yada-yada