Don't know if anyone is still following this rapidly drifting thread, but JIC:
After some further investigation, mostly in the Lucas 400e Master Parts Catalogue, I believe that the early cars had the wiper arms angled to park on the right (as seen from the driver's seat) only if they also had the driver on the right. LHD drive cars had the arms angled to park on the left. (Although of course as Lou pointed out, the motor itself did not "park", it just stopped wherever it happened to be when the switch was turned off.)
The exception is that early cars with 2-speed wipers had straight arms. They also used a DR1 wiper motor, while the later 2-speed setup used a DR3 motor. Both DR1 and DR3 could apparently be configured to park on either left or right, but at this point I don't have any solid evidence to indicate which one was supplied.