Several years ago I bought a set of small rear drums with large drums riveted to them. I was told they were an old aftermarket set up for using large drum Rocky Mountian brakes on small drum rear end. Well today I dug them out to put on a rear end I'm rebuilding and the Rockies don't fit, they are too small. Sure enough the drums measure just shy of 12.25" which is TT size, although they are not as heavy as TT. I don't know if Rocky Mountian ever made external brakes for TT trucks. I think there was a company named Bennett that made rear brakes for TT that worked even if you were going backward. Anybody ever do this conversion on their car or speedster?
Rocky Mtn. made brakes for trucks also. I think the original RM worked both ways, it's the newer style that doesn't.