Update for ’70 & ‘71 E-body, and ’71 B-body 2-Speed Wiper motor replacement:

Like cnxt said, the readily available/affordable parts store ’72 Charger(’73 Challenger) wiper motor is a direct bolt in and the ’71 linkage crank arm will bolt up, but is a bit loose due to the ’72 motor has a smaller shaft.

For me, this resulted in sloppy wiper action: The wipers wouldn’t cover as much windshield, and the would not park properly(wouldn’t hide away completely) – due to the slop.
Also, the ’72 motor shaft Parks/stops in a slightly different position (*this probably also attributes to not parking in the correct position).

Upon further investigation I found out the ’72 Crank arm motor shaft rectangular cutout is at a different angle than the ’71 Crank arm.
So, I purchased a ’72 crank arm(pt#3431553) on eBay to go on my ’72 motor. It fits perfectly w/no slop. Now my wipers work perfectly and park perfectly, - like brand new!