The 350 clutch was modified twice during the production run to try to stop the plates breaking, and the second modification includede a thick metal special outer plate. there was a further mod kit produced to partially update the early clutches, and this included a second different type of special outer plate. I've seen a Bridgestone Dealer Service Letter that gives all the details (including special part numbers) for these mods, but I'm damned if I can find my copy of it at the moment.
However.... I do know that the late type clutches used a thick, solid special plate. These clutches had the one-piece cast alloy pressure plate. If your bike is 1968 or later, it probably has this type of clutch.
Early bike clutches had a pressure plate with separate spring cups, and the special outer plate for these is thinner and hollowed out on the back. The two types of special plate are definitely NOT interchangeable.
I'm sorry but I can't remember which part number is which for the two Special plates, but I'll keep looking for my copy of the Dealer Service Letter and let you know if I find it.
