A local guy just bought a 440-6 4 speed 69.5 Roadrunner from the original owner.

The car has an 8 3/4 rear with 3.23:1 gears.

Story is that the original owner was working out of town in the early 70s and quickly grew tired of the 4.10:1 Dana on the highway so he installed the 8.75 with more highway friendly 3.23 gears.

Fortunately he kept the Dana in the barn for 40 some years.

I suspect this was a rather common occupancy back in the day.