I'm having trouble getting my wipers to work properly. I heard there was a stop motor within the wiper unit that sets the stop position. Has anyone heard of this? When I install the wipers and turn them on the arms drop down onto the valance rather thanstop at the bottom of the windshield...

Diag. Manual
"Parking Circuit: (Fig 12-28, 36)
Moving dash switch to OFF position opens both armature and shunt field circuits to ground at the dash switch. However, both of these circuits are still closed to ground through the parking switch.

Note: The shunt field circuit actually flows via dash switch back to wiper parking switch direct to ground which means that wiper is actually operating in LO speed during the parking cycle.

When the cam on wiper output gear opens the park switch contacts, the wiper is OFF and/or wiper crank arm should be in the park position."

It also says:

"BLADES DO NOT RETURN TO PARK POSITION WHEN WIPER IS TURNED OFF
1. Check wiper ground strap connection to car body.
2. Remove wiper from car and check for dirty, bent, broken park switch contacts."

After reading you issue again, did you install the arms with the wipers in the fully parked position?

Like Jimc says, it sounds like you need to remove the wiper arms, park the motor (it usually needs a little resistance to park, otherwise it just pauses)and reinstall the arms in the proper location for parked.

Not sure what year you have, but I found on my '67 that when the wiper motor is parked - you can attach the wiper transmission in two positions. Sort of like a distributor.

I would try disconnecting the wiper tranny from the motor, rotate the wipers through 180 degrees and reattach.

And I found that taping popsicle sticks or toothpicks to the ends of the knobs where the wipers attach to observe wiper motion sure helps to prevent wiper arms from tearing into the cowl panel area.