Dan,
While I haven't had my machine that far apart to check out your conjecture, I do agree with you. I think the operative word in your post is "lightweight" as the S&S crank weighs something like 43 pounds already, and with the Centa unit and shaft a lightweight flywheel and perhaps small diameter (though properly torque rated) clutch would be in order.
Whatever MMC uses for a clutch disc/cover it must be reasonably well suited to the task as that and the gearbox are about the only parts of the car that don't get a lot of failure discussion in the forum.
