If he likes the current look of the wheel in the opening, measure the ones on the car. It's easy. With the wheel flat on the floor, lay a straight edge across the wheel from lip to lip, and measure the distance to the surface where the brake drum/hub makes contact.

 

18 - 20 inch wheels look better on late model stuff. The vintage cars look best with vintage style wheels. Just my opinion.

 

I have 17's on mine. went with 275 in rear and I could have gone 295 (Almost positive). If I remember correctly I have 6" of BS on rears. I had this same conversation with 72Sat I am sure if you search the B-body section you can find it. If I did it over I would probably go 18 in back in 17 front, give it a better stance. Here is the link for last dicussion:
https://moparforums.com/forums/f10/s...s-wheels-2205/

 

That is a lot of air space around that tire.

 

There is, but the new tires are about 1/2" difference of the standard orignal tire. Plus its hard/impossible to find an inexpensive tire that size that would have filled that up.

 

Nah, read the next post. That is the finished look he was going for.

The problem is, trying to find a cheap tire and accepting that look. Just spend the money. You bought the wheels, now buy the tires that fit.