car has all stock location rear suspension and original rear housing and axles

how wide and what offset wheel will fit ,with as wide a tire as possible?

On my 68 Satellite: 15x8, 4.5 bs , 275/60-15 fits great

Assuming wheel wells would be the same 68 GTX to a 70 Satellite I have a 5.5 backspace on a 9.5 wheel. You can't get aggressive with a wide tire with that much wheel. I added a 1/4 spacer on the inside of mine to increase the clearances. I think 5" would be the most you could get away with comfortably.

I had a set of factory (Ramcharger?) 15x8 wheels on my GTX with M/T 275/60-15's. I liked them.

Stan

I think we cover this every week, but I like posting these pictures, I just think it looks so cool. 68 RT Coronet with 10 inchers and 4.25 back space, I'm gonna tell you it's about perfect. I have a set of 10 inch cop wheels with 5.25 backspace and the tires hit the springs on my 69 RT Charger, might work with a tire with less section width but I wouldn't go much over 4.5 back space to leave plenty of room and unless you go wider than 10 inches you will well inside the wheel well lip.

10" with 5-1/2 bs on my 69 RR

I run a 15x10 rear wheel 4-3/4 backspace with a 325-50-15 Nitto Drag radial on the rear of my 68 gtx. I do have the outside wheel lips rolled for clearance. You should be able to use a 15x10 wheel with a 5" or 5.5" backspace with 295-50-15 with no issues. I also run a 15x8 wheel upfront with 4.5 backspace and a 275-50-15 with no issues.

That's a lot a front tire.

what about up front?
15 x 7?

and tires, we like the solid raised white letter

T/A Radials
Goodyear Eagle ST

forspd340 thought 275/60's would work on the 8" rears.

what about the front?

or maybe do 15x8's all the way around?

with a different width up front?

car is manual steer

the 15 x 8's , is that all the way around?and same tire's up front?