I put 'em on my 70Dart back in highschool. So if the fit my Dart they will fit your Duster.
But I think 7" rims are too narrow.
A "G" is an 8.25 treadwidth, and the rule back then was to have rims equal to the treadwidth. I'm not 100% sure but I think I ran on 8.5s or 8s. But I have long forgotten the backspacing. That was about 1971/72.... I have even forgotten what my naked girlfriend looked like;completely.
