There are a number of different hub/drum combos used with various axles from the '40s through at least the mid to late '50s. You could swap the entire rear, or even just the hubs if your drums will fit.
Check out the swap meet section and post a wanted ad with all the correct measurments. Someone is bound to have the parts your looking for. I threw away a bunch of axle shafts a year or two back, all having different sizes and splines, some with a cap, others bolted to the hubs, but they were all pretty similar.
Jeff
