http://www.doctordiff.com/?page_id=41
DoctorDiff Challenger 1 1/2″ offset spring hanger/shackle kit for standard springs $175
DoctorDiff E-body 1″ offset spring hanger/shackle kit for Superstock springs. Can be used to bolt B-body rearend into E-body with no modifications $185
DoctorDiff E-body 1″ offset spring hanger/shackle kit for standard springs. Can be used to bolt B-body rearend into E-body with no modifications $175
All will require re-welding of the spring perches on the axle tubes, except the last one if using a 66-70 b-body rear.
When the leafs are re-located, then measure the current backspace of your wheel and go from there how much more you can go towards the spring and if a tire is one, how much more you can go to the fender.
I wouldn't bother doing a 3" axle re-location unless you plan on tubbing your car.
W/the above kits, you should be able to fit a 295 tire on a 10' wide rim. Backspacing is usually 6" w/the stock e-body rear, 5" w/a b-body rear.