1977 CB550 F1, the rubber is between the inner drive ring and the outer locating ring, probably 2mm thick and 20+mm deep. The 750 is the same part.
Don't know if early ones are different but the 1974 360's I have look the same as late model (except for 4 bolt rotors instead of 6) I have one lying around somewhere, I'll see if I can dig it out this weekend
PJ