[basketcase]

If you want to go do a complete C5 brake conversion that's fine and I'm sure the stopping power will be fantastic but Rreemo originally asked about rotors and rear axles for his '71 so he could mount his 4 3/4 bolt pattern Ralley wheels.

I checked a few things and find that both the C10 and G10 (van) use the same outer wheel bearing but they use a different inner bearing and seal, probably Impala size and smaller than the C10.

I looked up a 1975 Bonneville, which was still one of the really large ones, and found that both the inner and outer wheel bearings and the seal are the same as 1971 C10. So if you can confirm that the Bonne is 4 3/4 then you need to confirm that the diameter, rotor thickness and offset are the same. These specs must be the same or it won't fit your caliper location which can't be changed without swapping in another spindle.

They should both look the same laying side by side except the bolt circle. NAPA shows 3 different grades of Bonne rotors. A cheapo replacement for $41.; a premium one for $73.; and a high performance rotor for $114. It looks like you are on to something here.

Redrilling your rears is absolutely the easiest and cheapest way to go. Any machine shop can do it by drilling the 4 3/4 pattern between the old 5" holes. This is a common practice in street rodding. You could even do it at home if you have a good drill press and some carbon drills.

Of course the easiest way is to sell those 4 3/4 Ralleys and buy a set of truck bolt pattern Corvette Ralleys in a 5x5 pattern. That's what I'm using on my truck and like was said above they are about $60. each from Stockton Wheel or House of Wheels.

I guess it's up to you how much work you want to do. If you could find good used Bonne rotors (no newer than '76) you could probably come out cheaper all together.

Tom