how far can i move rear springs inboard with out geometry problems?

[bOb shingler]

get the tire and wheel combo now and set them in place with clearance all around. install home built frame rails. install springs in the frame rails just like mini- tubing. get a pair of 12 way adjustable shocks and install them straight up as possible.

 

[sccachallenger]

Many years ago I remember seeing a Challenger where the leaves were mounted to the inside of the stock rails. Wonder if you could build and then mount your new frame rails without removing the stock floor or rails, then mount the springs, and only after you're satisfied with the alignment remove only what parts of the stock frame that interfere with your tires. Might help you keep it straighter than whacking it all off first.