I'm having the same problem with the axle seal on the 64 axle I'm trying to put in Deb's 65. Had to special order it. I would say for sure now you have a 64 axle.

'65 C-10, 65 L-60, 65 C-80, 72 C-60 & and a bunch of old Chevy cars.
Never time to do it right, always time to do it over.