I dont know if you would be interested but I have a 1966 3/4 ton C-20 rearend not for sure on ratio,use to have a 4speed granny low hooked to it sale it to you for $300.00 dollars FIRM.NO SHIPPING on this pickup only.
I have a 77 c-30 rear end available. It is a 3.73 and has about 69,000 miles on it. I would take $75 for the whole rear end assembly.