I think that there are still R&P sets made for the Dana 44 rear axle since it was used in so many vehicles and forms of them are still being made today. The key would be whether the spline count on the pinion shaft is the same as for the early Dana 44 models for yoke fit concerns. I've looked around a little bit and found that you can still get them for a 1953 F100 rear axle which used the same carrier bolt patern and shared the 19 spline rear axle shafts the the Mercs, Ford police cars, and station wagons used. I know the axles and Dana 44 differential carriers interchange but the housings were just a little different for the spring mounting.
A person needs to talk to one of the outfits that specialise in rear axles to find out whether the pinions are different or not. For the 1953 thru 56 F100 there are quite a few ratios available but the carrier may have to be changed to use the lower ratio R&P sets. I just don't know for sure.