I had the perches cut off a B-body rear and new ones welded on at the 46 inch spec. If you are running a factory sway bar that is the way to go. Using offset shackles to move the springs will throw off your end link geometry.

No sway bar or aftermarket sway bar then the shackles are the way to go.

I'd suggest really planning out your wheel tire combo before swapping rears. I think someone makes a tool you can bolt to the axle and adjust to simulate different tire and rim combinations and then rotate it to see if it hits anything. Measure twice, swap parts once... or something like that