I am running a S-10 rear in my 41, you do need the 4x4 rear end. I checked a lot of them for their gear ratios, a lot were 3.73, but some were 3.08. seemed to me the 3.08 gears were in the latter trucks, with the 4.3 motors. At least that's the way it seemed to me. I used the 3.73 in mine, w/ a T-5, and 261, works great.