I'm considering an A 500 4 speed overdrive for a 72 Duster

The 200 has an all one piece case like the 904 and 727 so it has a dedicated bellhousing. You have to use an adapter plate kit for it to work on a Mopar. It's an added expense for sure, but the end result is you don't have to cut the car if you don't want to.
Thanks for some reason I was thinking the 200 was a manual transmission.