I have a 1956 ford f100 and I'm trying to replace the rear differential gasket but I don't know the specs for the torque to put the cover back on and I can't find them anywhere. If someone could help it would be appreciated thanks in advanced

 

Generally speaking, AFAIK diff covers are like valve covers, only needs to be tight enough to keep it from leaking. If you crank them down you're warp the cover.
Unless its something other than just a cover, like the differentials where the ring/pinion and whatnot are all mounted to half the diff that drops out of the axle, in which case it probably has an important torque spec.

If you're using RTV on the gasket, its probably finger tight, then wait a couple hours/overnight for the RTV to set up, then tighten down a bit more with the wrench.