The flywheel in the old single overhead cam motor differed somewhat from the Quartermaster flywheel required by the SCCA for Formula Continental. Consequently, the pinion gear on the starter must be harmonized to meld with the new flywheel.
The pinion gear on the older starter is seen at the right in the photo above. 9 teeth.
Primus Racing Parts had a used starter for sale. $125 plus shipping. They were very careful to determine whether I was using the starter for the older motor or for the Zetec. That is because the starter, when used for the Zetec motor, must have a 10 tooth pinion gear. The photo above shows those ten teeth. The Hi Torque Starters are identical. Thankfully Primus wanted to make certain that I was going to have a pinion gear that meshed well with the Quartermaster flywheel.