Guess on gears in a '74 318 Duster with 8-1/4 rear

DusterDaddy said
This is friggin bizarre!
Jacked up the rear, car in neutral, rotated right rear wheel 1 full revolution. Driveshaft turned 1-1/8 full rotation.
WTF?

That is because your rear end is a open differential. That method works on SG rears. What you are encountering is the spider gears turning.