Tim,
I believe in '53 the 3/4 ton front axles changed to a thrust bushing. '52 and earlier had a thrust bearing. The bushing being much thinner than the bearing, the difference was made up in the length of the king pin boss area on the axle, if that makes any sense.
I have both style axles and have compared/studied them before. I'll take another look at them tomorrow to make sure.


Steve

'49 3800
'52 3600
'57 3100