7 1/4 rear brake question

Hi guys got a question brakes on a '76 Dart Swinger /6 3 spd overdrive. It has 4 wheel drum brakes with 5 on 4" bolt pattern. Did this model come with 10" rear. According to Rock auto listing the Swinger came with 10" drums on all corners. The rear was swapped out for and auto rear with 9" brakes a few years ago. We have the original 3.23 rear in pieces which had 10" backing plates but when we took the axles to the machine shop he told us the bearings were for 9" rear brakes and may not work with this rear. Will the 9"brake bearing cause problems with 10" brakes. Did this car come originally with 10" or 9" brakes? What the difference between the two size of bearings?
Thanks
Guy