Some parts sources list the HO33 differential as a "55T", meaning "55 Truck". The same sources also tend to list a "55P" for the '55-'64 Passenger differential.
As far as finding a cross shaft, you might try Toms Differentials. I beleive they do have them, and theirs is made to eliminate the block in the diff assembly. I'm pretty sure it is designed to work with the stock axles, as well as their 30 spline conversion.
