I believe the reason no one has sought a "beefier, more efficient" clutch is there is simply no need to do so.
As for you comment "the Morgan 3W practically has no flywheel" you need to remember that that S&S motor already has a huge amount of mass (and therefore flywheel effect) in it's 43 pound crankshaft. Adding any more mass to the rotating assembly, especially cantilevered from the crank as is the M3W clutch, is a very bad idea, IMHO.
+1
