Pretty cool thread. I bought a mint rim-blow out of a '71 Dart in a local Michigan junkyard in the mid-80's. Still have it. Car was Bahama Yellow - I remember that. I have no idea what the drivetrain was. I was captivated by the steering wheel!

All 8 3/4" axles after mid 1969 were the '489 casting regardless of what car or engine was in front of it.
The front disc and 8 3/4" axle was part of a towing package option group. I'll bet Barry/Alaskan T/A can verify this. I have seen more than a few 71 and 72 4 door Darts and Valiants with this axle. The slant six seems odd for towing but they did build them this way. Also look for a 22" radiator that you'd rarely find on non A./C slant six cars of this era.

That was my point, how did a 71 car have a 741 with a small pinion as the Op suggests?

741’s came in A-bodies after 69. I believe this has been discussed before.

Here?, because the reply I quoted states differently, and don't mean to beat a dead horse, but I would like to be sure I have a definitive understanding.

Dang, what a cool find! Congrats! Cool options too!

I parted out these cars both which had 8.75 741 rears.
A friend has a 72 Duster that he bought from the original owner that has /6, 904, A/C, power disc, 8.75

I agree
The 8 3/4 My wife and I got out a 1970 or 1971 Dart Swinger 340 4 speed at a yard had an 8 3/4 SureGrip 355-1 missing one drum.
We took it out was 100 bucks. The guy said let us know when you get it out and he had a yard guy come to bring it to the parking lot and place it in my truck since it was a large item.
When I paid the driver said ya know it is missing one drum so he and my wife said well? So the guy said OK $80.00 Cash.
It was never busted up prior to me it still had the 355 id tag and