You can see one groove, there is a suggestion of a second groove (which 2 would denote an M20), but it's not clear. If the pic was shifted forward about an inch you could likely see for certain. You know it's a 1" cluster pin Muncie, '68 likely.
Doesn't appear to have a suffix on the build code, looks like an "8" to me. What an eye - stretching exercise -
Better pic of the input and you can figure this one -
Regards,
Steve