hmm, knowing me i would propably rebuild the 8.5 inch just to know that its in perfect working order... c-clip eliminators would be next... the safe bet is propably the 12 bolt.. especially since my bear brakes have ford brackets....
the 12 bolt seems to be alittle cheaper too, its the same price as the 9 inch.. but it doesnt require a centersection... and id propably go fro am aluminum CS just because it was available....also its 33 splines instead fo 31