On the very early clutches the fiber plates were thicker, 3.5 mm and had rubber O-rings between them to help absorb some of the shock of engagement.
The mid years used 3 mm thick plates and left out the rubber O-rings. They added another fiber and steel plate to make up the extra space.
The later added the spring loaded plate on the hub and deleted a fiber and steel plate.
I haven't used the very early clutch so I can't say much about it. I have used the mid year and later clutches on my 750 kitted 75. The main difference in feel is the mid year clutches engage a bit harsher on initial take off but once under way you won't feel much difference.
The later clutches have the spring loaded first plate that absorbs this harsh engagement so you notice it a lot less on initial take off.
One thing I di recommend is that which ever way you go look at the steel plates, they are stamped out. This leaves a rounded edge and a sharp edge. Use a 150 or so grit sand paper to break thus sharp edge, make it match the rounded edge. This lets the plates slide easier on the hub and basket. You can check the fiber plates for the sharp edge and remove it too.
While sanding the steels sand the entire surface to remove any discoloration and rough up the surface. This will improve the grip.
I replaced the worn clutch springs with new 70 lb. Kibble White springs. The stock were around 50 lbs. new but after 35+ years I doubt they were even 45 maybe 40.
Use a well lubed cable and worm, proper adjustment and it should work well and a two finger pull, mine does.
No slippage under the extra power of the 750, easy to pull and find neutral, what more can you ask.
Leo
After a bit of trial and error I finally replaced the clutch plates with Forodo plates.