I agree with what's been said reguarding the spacer plate. They are hard to mix up and pretty obvious when you go to stab a starter. Sounds like it is bolting up. If you have to force the starter -at all- to fit, something is wrong.
Don't quote me on this Mark, but I believe just about all of Fords starters used the same teeth count, at least through the 60s and 70s. Was 10 teeth, wasn't it?? I do recall changing out the cone portion of the starter with that of an FE starter (3-bolt) and it worked fine. this may not be true for all though.
However, I have seen SEVERAL different depths of starter drives. The depth seems to stem with the aluminum cone that houses the gear end of the drive. I usually buy re-man starters that typically end up with old reconditioned factory starter cones. These seem to work better than the aftermarket replacements you will find on 'new' (not rebuilt) starters.
D2AE, D2AF, D0OE are a few examples of part numbers found on the aluminum cones that should work fine, for either 141, 157, and 164 tooth flexplates.