The G.M. rear end up through 62 was a whole different animal than the latter models. 3.90 is the highest ratio they used except for a few 3.38 in 59 which are very rare. The after market produces a 3.38 gear set. They were unavailable for about 2 years but are readily available now. When we couldn,t get one for my partners 60 panel we installed the complete rear end from a 70 model with 3.08 gears. We had to buy a bracket kit & special panhard bar. It worked good but I would rather change the gears.
