1973 duster wheel bolt pattern

Honestly, i would have gotten a '68 - '70 B body 8 3/4 rear and just moved the spring perches in 1'' on both sides.
I did this with my '74 Dart Sport and am very happy with the results.
With this swap, it is a lot cheaper than getting an A body rear housing and then buying axles etc.
And you get big bolt pattern automatically with this set up..........what's not to like?
As far as wheels, i have factory 15X6 1/2'' rallye wheels and 255 60 15s on my car and with the right offset wheel, i could easily fit 275s in there. I did roll the inner wheel lips in just to be sure and it looks and works great.
The Duster/Dart Sport wheel openings and quarters are the same, and you can fit a pretty good sized tire in there without mini tubbing or moving the springs inboard.
I personally think that the stock width A body rears on these cars with stock wheels looks too narrow, and the B body rear gives the car a better look as well as a wider track.

As for the '73 and up cars brakes, all slant six cars with standard non power brakes were small bolt pattern front and rear.
All cars with power brakes or a v8 got big bolt pattern front and rear with front discs.
All of the '73 and newer sbp slant 6 cars that I've seen had 10'' front brakes with a finned drum.
Also, all cars built after December 31st 1975 had big bolt pattern and front discs regardless of power or standard brakes or engine ordered.

This info has come from many years of personal research and looking at literally hundreds of cars and parting out several as well..........
I hope this helps,
Tom.