Back spacing on B body rear end in 73 Duster

Duster looks good, from the research I was able to find here and other sites the later b body rears are little wider than the earlier one's so it would push the wheel out further allowing more backspace than the earlier b body rear. Mine I just put in was a 66 or 67. Don't know on how the wheels will look yet as I don't have the diff set up yet to install the axles, but will use that formula on the 8 inch wheel with the 5.75 backspace if the one's I have don't look right.