If I remember correctly, the 1/2T (C10) trucks used a different rear end than the 3/4T (C20) Trucks.
Chevy made two version of the 1/2T differentials, the 55T and 55P. The "T" was for the trucks and the "P" was for passenger vehicles (cars).
This was not used in the 3/4T trucks.
Here's a link to the
Diff Wizard on the
www.ringpinion.com website.
You should be able to plug in your information and see what fits, and what's available. I know they sell 3.38:1 gears for the '62 1/2T trucks. I don't know what they may have available for the 3/4T trucks.
I have done business with Randy at Ring and Pinion since he was a single mechanic working out of his garage in Sacramento, CA back in the late 70's. He's done well for himself and treats his customers fairly. I recommend him.
