Whos running over 700whp on an 8.75?

I think if you have the D60 already and all it needs is shortening and flanges/brackets welded on your answer is easy. Use the D60. IMO though at your power level even a stock D60 won’t last too long. You need a fairly well build rear end. I looked at quick Performance stuff a while back and you can put together a pretty beefy 9” that will hold 1000+ hp for about $2900.