Why not use offset spring hangars, and roll the outer lip before u try to measure anything ? U can very carefully cut a rear spring pad in half, (DID MINE ONN A BIG BAND SAW) and weld half of it to each side of the existing pads on the axle. u won`t have to mess w/ getting it right or out of whack. u then redrill the u bolt holes for the offset, the rest is bolt together stuff. U could end up w/ about 1 3/4" more room. I did it and have 295 65 15 drag radials on a 68 barracuda , which have very small wheelwells to start with. I did lengthen the front edge of the wheel well before paint tho for the tire heighth .
