Gear Vendor OD Blues RE: 73 Duster

I helped a friend install his, he had a 74 Dart sport. (pretty much the same thing as a Duster) All we had to do was the same as @abodyjoe mentioned above.
I ordered a GV as well to put behind my A999, I'm just waiting for them to get some A904 tailshafts in stock so they can ship it to me.
I wouldn't be too quick to blame GV. You've stated that "A few hammer blows as so many forums indicated does not apply to this A body!" That there might be an indicator that something's off.
GV specialize in drivetrain OD's, I imagine they're not all knowing when it comes to things that deviate from the "norm" (basically stock parameters).