Sorry Larry, I looked on Randy's site and I guess my truck would have a 8.25" rear end, according to them. My owners manual states 8 3/8 as well as service manuals. My 1975 service manual has 8 1/4. Not sure if the 8 1/4 and the 8 3/8 rear are two different units? I have seen the reference to both... but I'm thinking they're basically the same.