8 3/4 pinion splines

Let's stop guessing

742 - (1964-72) 1 3/4 pinion coarse spline
741 - (1964-69) or 657 - (1957-64) 1/3/8 pinion coarse spline
(1969-72) 1 3/8 fine spline
489 or 488 - (1969-74) 1 7/8 pinion coarse or fine spline

While I'm at it:
Sure-Grip - Dana PowerLok (clutch style) 1958-1969
Borg Warner Spin- Resistant (cone style) 1969-1974