“I was wondering if the L/U had maybe been swapped out at some point, from an earlier motor?
The motor itself is stamped in both ID locations as: 15020-08457”
That looks like what happened Bill. The manual for ’57 shows motors up to 07000 used the pin, after that the screw/pin. Your ID shows it’s the later ’57 that would have the screw. The manual shows both in their diagram.
