I just went through the same dilemma. Rebuilding and restoring my 69 GTO I got it in pieces. It was a true "tree-line" car. The wheels that came with your car were most likely 14 x 7 and they used a G78 or in the case of a wide oval a G70 tire. The G78 is very close to a P215/70R tire of today. In fact I believe the P215 is overall about 1/2 inch higher after being installed. Width, I believe, the same.
With the car I got 1-14 x 7 wheel and 3-15 x 7 wheels. I was going to do the same thing and put a 15 x 8 wheels on the car and while working with Performance Plus Tire out of Southern California, their most knowledgeable sales rep. (in my opinion) named Andy recommended against it. Oh, and by the way... I found them to be the best overall buy. Anyway, if I tried to stick to the same tire with the 15 x 8 it would have bulged or ballooned the tire to a point that it wouldn't look as good. I didn't want big wheels and tires because I wanted the car to look as close to stock as possible, but had already decided to go with a newer style wheel vrs. looking for the Rally II replacements. I thought the investment in rebuilding (sandblasting and repainting) Rally II's or buying new was better spent invested in new classic rims.
I went with a set of 15 x 7 "32 Keystone Klassic Chrome Wheels" and a full set of "Silvertown Radial 2 Redline (redwall) tires". The wheels ran me $752 for the set and the tires weren't cheep at $916 for all four, but then... I wanted it to look nice when finished.
Oh, I did have to buy a set of chrome lug nuts at an additional $29, obviously.
My short answer... yes, they will work, but after giving it some thought, I decided to stay on the safe route.
Another thing... if you're really unsure, you might want to invest in a Percy Wheel & Tire Fitment Tool. They're about $75, like this one... http://www.summitracing.com/parts/php-01201