I know what you're saying and I've been giving it some thought. I am going to write Olav Aaen and ask him for suggestions. I'm pretty sure he would have some ideas. Machining a new top shaft for the chaincase wouldn't be too difficult, the problem as I see it is that any secondary clutch other than the old ones that run on the right side of the chaincase wouldn't work. Any modern secondary would be spinning in the opposite direction it was designed for and it's torque sensing abilities wouldn't work anymore, at least in my mind. You'd have to machine a helix completely opposite. Not an immpossibility either, just the cost involved. But then, like you say They seemed to work then.
I had a 71 SL 338, my 71 SS 433, a 72 433 B, 74 GP 433 and 75 GPX 338 and I never had a hitch of trouble with any of the secondaries. The primary spring seemed to get weak quickly, but the secondaries in all of mine worked like a charm. Of course I never tried to push the power through them that I am planning on now. Maybe somebody else has dealt with this before? G.