Would the 17x7, 4.25" backspacing fit on a 1st gen stock suspension and what size tires?

Moving leaf spring mounts on 66 Can you move the front and rear leaf spring mounts inward, narrow the rearend and widen the inner wheel wheels to make room for wider tires on a 66. Would I want to? How close together can you put leaf springs so they will still do their job correctly?

I used the Percy's Wheelrite fitment tool to see what I could squeeze into the stock rear wheel wells of my 63 hardtop. For those of you who have checked out the wheel fitment threads before, there are no real surprises here: 15 x 7 with 4.5" backspace, or 15 x 8" with 5" backspace seem...

What is the widest wheel I can fit in there without too much rubbing issues? I was thinking 15x8??

What size front rims and tires are you running on your 1st gen?