The weak link in any of the J-bodys drive train was the 7 1/4 rear. The 8 1/4 rears didnt hold up too long for me either. The factory leaf spring front oval eyelet was another weak point. I would snap the driver side leaf spring, right after the eyelet. So for me stepping upto an 8 3/4 with super stock (SS) leaf springs was a neccesity. Eliminating the iso-crap was by choice. Those rubber pads held water and rust out the iso-clamp parts.
As far as the U-bolts go, try to find ones that have a flattend part in the U itself, this will avoid crushed or distorted axle tubes. I have distorted passenger side axle tubes where the U-bolts retain the housing. Aftermarket Green bearings arent forgiving on a bent housing and wont last long.