Yup that would be the next consideration, the starter. Could check the action of the starter gear, make sure the solenoid is pulling that gear all the way forward, no obstructions on the shaft. With the starter out, the lug that is on the bottom of the solenoid, disconnect that so the starter dose not spin the motor and then apply bat V to the solenoid and watch the action of that gear in the nose.
It sounds like you have two different starter sitting there if I am reading the post correctly, could have mixed them up, would not be the first time that happened. Not major but none the less a PITA, starters are no feather weights.