I recently just bought a projet rig. Its a 1977 C-10 Custom Deluxe 2x4. I mainly bought the the truck for the engine, it being a 400 hp, four-bolt main. But now im in the restoration process. Whoever owned this truck before is a strange person. Orginaly, the truck was a 4-speed manual tranny. Then they replaced that tranny with a 3-on-the-tree. Now it has a "pro-matic" tranny and shifter, which I am not partial to.

Im trying to either figure out what size tranny I need (gear-ratios) for this engine and restore it back to a 4 or 5 speed manual tranny. If anyone could be of any help, I would greatly appriciate it. Thank you.