It seems most parts houses show the bolt on lid master cylinder for the 70 Duster with 10" drums and the master cylinder like is shown in my picture above for 71 Duster with 10" drums. Why the difference?
The master design change from a bolt on lid to one with a bail , but it has 2 equal size pots. Also I'm pretty sure drums masters have a built in residual valve that the report of the disc drum master does not.
Drums look like this
https://www.rockauto.com/en/moreinfo.php?pk=309083&cc=1231939&pt=1836&jsn=875 ... this is listed for a 1971 Duster doesn't say 10" or 9" but it does have a bore size that is bigger than a 9" listed master.
I just looked at rock auto and they have a bunch of disc masters listed as for disc OR drum ... after my experience with them having the wrong shocks listed for my 98 Ram 2500 and them thinking that they can't possibly have a wrong listing so I had to pay return shipping for their F'up... I don't have a lot of faith in their listings.
