Which company for narrowing a 29 spline 8 1/4 rear end

IMHO if your truly going to have 400hp, then go with a 8.75

The cost of shaving down that 8.25 and re-splining the c-clip axles would just not worth it to me, If I were doing the same thing.

Personally I took a CBody rear cut it down and had the axles re-splined years ago so that I could have the large bolt pattern axles and 11" brakes and came in at under 1000. But now I have a plenty strong rear I don't have to worry about plus I can chuck in quickly whatever geared chunk I want.

However if you do go with the 8.25, I would be really interested in seeing a build thread here with picks for sure as I'm sure many would. The steps and learning would be great!