Has anyone used a wheel spacer to fill in the rear wells on a Duster?

Of course, you could install a 66/67 B body 8 3/4 axle.

That puts the rear track perfectly in line with a front A body disk brake car track.

You would solve at least three issues with hat-

Track

5 on 4 1/5 lug pattern

8 and 3/4 axle