Sounds like the drive arm is at the wrong angle, on the box on the end of the motor. I had one slip on my Model A, did the same thing (Newport Engineering too).
If you had the motor on the wrong side of the 'arm' to the wipers it would try to turn the wipers the wrong way when you turn them on (down into the cowl
).
Let us know if you find out something different, I have a Newport setup to put in the '50 I've got, but it's still in the box (or I could give you a more specific / detailed answer).
