willy the same rear axle assembly was used in 3/4 & 1 ton trucks from 1947-72 any of the third members will swap into any of the axle housings. 4.10 is probably the best you're gonna get. only other ratios made were 5.14 & 4.57. gm never made any thing else for this axle. an aftermarket 3.9 rring & pinion was produced at one time but know more haven't heard of anyone finding one anywhere. 1 tons usually have 5.14s, 3/4 tons usually have 4.57, unless its a V8 atuomatic truck then theres a good chans it's a 4.10. mine come from a 67-72 gmc 350 atuo truck
