What bellhousing do you have? Did you replace it with this engine work you have been doing by any chance?
Flywheel: parts book says your 157T C30Z-6375-E flywheel should be stamped #C7ZE-A. Gotta look carefully for this around the outer edge. 1/4" tall stamped letters, not cast.
(If you find #C7OE-A it should be a 164T ring gear.)
Starters: Book shows this, for 1965-1966 289MT C20Z-11002-B is replaced by D40Z-1102-A (SA-660) which appears to have been replaced by E4DB-1102-B (SA-734B). That is a 1984 starter that you should be able to get easily. The SA-734B is an industry interchange number of some sort.......
The short story, is that there are basically two types of small block starter noses in this time frame, a short one, and a long one. You need the longer one, but something else appears to have changed.........like a bellhousing.....or so....
I confirmed that the bendix drive gear is the same on almost all starters except for 6 cylinders. Small block to big block all use the same piece.
Again, give me a call if you can, or look me up in Reno tomorrow....