John,

If you are referring to a 3100 (1/2 ton) enclosed driveshaft rear-end, Patrick's in AZ makes a 3.55 ring&pinion replacement (and separate bearings/bushings/seals installation kit). Almost all thew reproduction parts vendors sell Patrick's 3.55 gears, but call Patrick directly and ask for a Stovebolt.com discount (because you have read such nice things about him on this discussion board).

http://www.patricksantiquecars.com/