Original Rear end type on my 70 Duster

Absolute baloney.

All the big block A's came with an 8 3/4".

Same for all the 340 A's.

Same for any 1970 up A with a 3-speed stick.
Interesting.... Everyone knows that no 340, 383 or 440 car came with a 7 1/4" axle.
You are cherry picking, Barry.
"Standard" was in reference to base model cars before any options or optional models were chosen.
If you're so smart, where were you yesterday to offer your wisdom? You just sit back and wait to jump in when you think you have to TRUMP someone?