I was hoping to find a transmission manual on line at the old chevy manual project site, but could only find 3 and 5 speed along with automatics.
I am sure someone will chime in on the subject. But just wanted to relate a story about my 1952 Willys transmission. My brass syncro rings went out one time and I took the transmission out with the help of my manual. It wasn't hard to take it apart. Once I replaced the syncro rings and put the transmission back in and reinstalled it would pop out of gear. So I took it apart and the only thing I could find was there was a thrust washer on the back end of the cluster gear shaft that was a few thousands out. Got a new one and installed it, and that was the problem.
I would try to rebuild first if the gears are in good shape. If the gears are bad I am sure it would be cheaper to find another one. Good luck.

A day without laughter is a day wasted- Charlie Chaplin
When wrestling a grizzly bear, you have to keep at it until the bear gets tired, not when you get tired.
1948 Chevy 2-Ton