I had a similar issue with my New Port electric wiper motor in my '50.
The control arm on the motor was clocked wrong from the factory.
It is splined and can be repositioned by backing off an Allen screw. Takes a bit of trial and error to get it right.
I found that moving the passenger and driver side wiper transmission to their furthest from park position was the best way to confirm that the control arm of the motor was clocked correctly at the furthest from park position.
The best way to get the control arm to the furthest from the park position was to turn the motor switch on (without the wiper transmission arms attached) until it just reaches that position and quickly remove the negative battery wire from the battery. (Shutting off the switch will automatically return the motor to the Park position which does not help at all.)

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission