The 39 3/4 ton axle is the same as the 39 1/2 ton. 1/2 ton axles should be straight bolt in through 1954. Not certain about 1955. Did they change the track?
I tried to verify that the '39 ¾-ton and the ½-ton have the same part # in the 1929-54 MPB. According to the book, a ½-ton is a series JC, a ¾-ton with 11" brakes is series JD and a ¾-ton with 14" brakes is a JE.
I cannot find an axle listed specifically for these models but I do find one for '34-40 Comm. and another for '41-54 ½-ton. From that I'd say Gary needs to find a '34-40 axle for a bolt in replacement. The '41-55.1 may be usable with some mods.
