I didn't mean to imply the 160 and the CB77 had the same size drums....I meant that series of bikes used the same front and rear size drums....meaning 180mm front and rear for the 160's and 200mm front and rear for the CB/CL77.
About 30mm wide for the CB/CL77 drums. But LONG shoes with lots of contact if braking power is an issue.
I think around 69 Honda went to a smaller rear drum for all their bikes when compared to the fronts.
I went and grabbed a CB350 front and will marry it to the hub I have. It won't take much machine work. He also has a CL77 with a back wheel and is going to blue wrench it off for me. I think what I really need is to be found on some Italian bike. I snapped a few pix of a few things there.
It's not really within my realm of knowledge to modify shoes other than having them relined with race compound and arc'ing them to fit drums.
The CB350 (front) shoes are 1.4" wide, the GT750 (front) shoes are 1" wide.
As for strengthening the plate...really shouldn't be necessary...the hub maybe yes, but the backing plate isn't going to see any forces it shouldn't be able to handle. Since the backing plate doesn't see any of the bike weight, or drive torque, just the braking forces (which would be determined by the shoe size) it shouldn't be under any more stress than it would be on a stock bike....with the exception of extra heat developed stopping a larger bike. Modern compound shoes like Fedora should handle that.
Actually I'm still not real clear on what you are doing as far as matching things up, or the end purpose of the wheels. I've just been looking at all the cool pictures