Tranny spline count?

I have a 92 with an AW4 and 231. What is the spline count on this setup? I am looking at buying a newer 231, and want to make sure they will mate.

I know the earlier years use 21 splines, and later years use 23. What year did this change occur?

TIA

To the best of my knowledge, the 21 spline is for the 4 banger and the 23 is for the 4.0.