Topic: Difference in CB750 rear drum plates?

[srook]

I have a 1971 CB750 project that came with 2 rear drum plates.  They look identical except for some subtle differences.  One has a longer brake arm than the other.  The longer one is not smooth all over it has a recessed area that is rough.  Which plate is the earlier one?  The bike came with 2 rear wheels a 16" and a 17".  I assume the 17" is off the later CB750 and the 16" is something that someone did to it in the 70s.  Any help is appreciated.
Thanks
Scott

[Clyde]

The CB750's came with 18 inch rear wheels for the 69K0-76K6 and 75F/76F1, with chrome steel rims.
The 77K7 and 78K8 used 17 inch chrome rims on the rear.
The Automatics (76-77) had an aluminium 17 inch rim on the rear.
The 78 750A  used Comstar type 17 inch wheels and the F2/F3 used 18 inch Comstar wheels.
Honda changed the brake plate a few times mainly to do with the wear indicator.
The Automatics had a different brake arm which has two ribs (recessed?) rather than a smooth lever. A photo would help to positively ID the arm/plate