narrowing a b-body rear

LOL, yeah, that's what I have heard from many others. Although some said why even relocate the perches? the mounting is what, one inch total? That comes out to 1/2 inch each side? That would definitely be the least expensive route, as the perches are still there. I have some cop wheels, how much room would I have? Do I measure the backspacing from the 14 inch OEM wheels and compare to the 15 inch wheels? Then the other measurements? MY GOD!!! So many questions! Thanks to all.