A904 front planetary and washer question

Do not mix 904 planetarys with 998/999 mainshafts and vice-versa. The mainshafts have a different spline configuration while spline-count is the same. If you install the wrong mainshaft it WILL fit ........ But in a few miles Ziiiiing the aluminum splines will tear out of the planetary..... and then you'll be walking.
Actually I think it was an across the board change in the 80's. In which case it would mean ALMOST the same thing; If you need a planetary, and don't have a donor trans, you are gonna need to match the years carefully, to avoid the dreaded spline-failure.
I seem to remember MoparAction did an article on this.