Back spacing on B body rear end in 73 Duster

Just trying to figure out the best route to go I have a B body 8 3/4 I am putting in my 73 Duster, and want to know what backspaceing I should use. I want to switch to 15 X 8 ralley rim.

Good post, I just did this 2 days ago, haven't installed wheels yet, still waiting on parts to arrive and to set up the diff. I put in a 66 B body that is supposed to be the narrower of the B body rears. :blob: