the big bearing's also use a bigger bolt to hold the backingplate/shaft in...
somewhere like 1/2"? and the small bearing use something smaller...
i remember now on mine - the shafts are retained by 4 bolts that take a 3/4" socket - so the large bearings are the 1/2" bolts....
FWIW -
1976 f-150 rear end, 31 spline, big bearing, 3.50's, open, 5 on 5.5, 11x2.25" drums, standard pinion support, standard case, not sure on carrier bearings yet (havent had to measure), 65" WMS at full width.
5 on 4.5 can be drilled into the flanges fairly easy, however, you will have to look into explorer brakes or whatever else after that...
thanks Gil - i had forgotten about the bolt pattern change/width issue...
My 9" works for me...