The internal parts that wear are interchangeable such as the synchronizer and shift forks. Although the case has the same casting number, the internals changed around 52 or 53. The early one can be identified by 2 lugs on the synchronizer and the later one has 4 lugs. Synchronizers are getting very hard to find. If you are lucky, the passenger transmission has a good synchronizer. If your transmission has 2 lugs and the donor has 4 you can grind two of them off and it will work.
