So, I reconsidered the idea of the 8-3/4" with this big a tire and the eventual 650-700hp big block. Found a narrowed Dana 60 a few hours away for a decent price with trac-loc and 3.73 gear, had to cut off the brackets and pads it had welded to it.

Took the 8-3/4 out, cut the spot welds off the axle brackets and fit the Dana in its place. it is only an inch narrower than I had planned to cut 8-3/4 so just some 1/2 spacers will all it may need.