Probably the incorrect starter.
Ford had 157 and 164 tooth starters. 164 was for older manual cars.
the 164 was only different in that it has a longer snout for the older cars, where the 157 tooth fly/flex wheel starters are the same on later cars. The diameters are different on 157 flex/fly wheels but the mid plate that the starter bolts to will keep the starter the correct orientation.
Why was the original starter replaced?
^that should help clarify it a bit.