How to Narrow an 8 3/4 Rear End

May i ask why shorten the axle if doing the 3 inch inboard relocate? just weld new perches inboard like mine has and i fit a 295 65 15 easy.

That works fine if your wheels have the correct offset. If they don't have the right offset they won't sit where you want. I'm narrowing mine 1" to pull the wheels in where I'd like them to sit. When using the larger brakes it brings the wheels out 3/8" on each side, thus another reason you may have to narrow the rearend