which rear to use for autox?

I'd use the 8-3/4 but keep the stock axle bearings. The 8.8 rear is an ok rear if your not making big power but unless you install a C-clip eliminator I wouldn't even think of it. The 9" can have either style of bearings, tapered like a 8-3/4 or roller bearings like Green bearings. I've torn apart a few 9" and it seems hit or miss as to what you find.