Steve, from what I've read Eaton was the rear axle used for many years. There was a good thread on stovebolt identifying these axles. Unfortunately they have upgraded their software and for the time being it does not appear to available, I'm checking on it.
Look on the passenger side front of the rear axle tube near the pumpkin, I believe you should find model and ratio there, see if the models are the same. I haven't read of any problems swapping other than splines, maybe. Wish that thread was there.
I found the thread it seems to confirm that you can use up to a 72 Eaton in your 50s truck.
http://www.stovebolt.com/ubbthreads/ubbt...=true#Post84246 Larry
