The diameter difference is because one is a 2:45 1st gear and the larger is a 2:74 1st gear. All the low 1st gear sets that I have seen use the longer splines because the low gear set models were all 4 clutch as far as I know.
Both of those are not low first gear sets. They are both for a 904 and both 2.45
One on the left is a 67. The one on the right is 76.
The diameter and everything on those two are the same.
The only difference is that the splines are higher in the 76 and it has that ridge on the inside. You can’t se it that well in the picture. I’ll see if I can get a bigger picture.
