Ultimately the easiest thing to do is to find the widest tire and wheel that will fit and then buy them first.

Your only real backspace considerations need to be what you will see from the outside...some like little backspace and a short rear...personally I like a rear that would be a little shorter than stock and then sticking with a near 50/50 wheel offset...maybe even more back space when using a wide wheel.

Depending on your wheel well opening 30" or so tall is the limit without modifying the 1/4's.

I run a 30" tall tire (275/60/17) on a 9.5" wheel with 5.5" of backspace on a stock wheel well on my 70 Satellite.

I have the leaf springs moved back 3/4"...I think the section width of the tire is about 11.75".

The springs are SS springs and I have the front hangers flipped upside down...I also installed a 1 1/2" lowering block between the spring and the rearend perch...

It is stuffed about as full as you can go without relocating the inner wheel houses and the springs.

Buy the wheels and tires you want...mock them up where they fit in the wheel well the best...

This will determine the width you will need for the rear...don't forget to figure in for rotor and/or drum thickness...

Then decide if you want to use leaf springs or go with a 3 link or something...

Ride height can be modified using leafs by installing the front perch up or down and also by using sliders at the rear instead of shackles...

This how mine sets with about 150#'s of stereo equipment in the trunk...