This is an easy swap.
I did it for my '74 Dart Sport and it was simple.
You just have to move the spring perches toward the center 1/2'' on each side making them 1'' different than the B-Body factory mounting spot.
You can get new spring perches from Dr. Diff for like 15 bucks, so that part is cheap.
BTW, the Dart Sport and Duster have the same room in the back, they are built on the same platform '70 to '76.
The great part of this swap is that you automatically get the big bolt pattern axles, and the housings are a lot cheaper than the A-Body ones, plus you don't have to buy axles.
I used a '69 housing in mine so it is slightly wider than the '66-67 you have.
I run 255-60-15 tires on a 15 X 61/2'' factory rallye wheel and have enough clearance that i could easily run a 275 width tire with the right offset.
As it is, I have about an inch and a half clearance between the inside sidewall and the spring, and about an inch to the wheel lip which i rolled up to be safe.
I also used 002 and 003 Super Stock springs on my car, but that doesn't really matter here, unless your springs are sagged badly like mine were, that's one of the reasons that i rolled the wheel lips in initially.
I have some detailed pics in my build thread if you would like, but it looks like 318 willrun has it covered for the most part in his video in post #6 other than cutting off the perches and welding new ones on, which is what i would do especially if you have new bushings in your springs..........
The link is at the bottom of this post to my build thread if you are interested.