I had the same thing going on with my 65 Rocket. Ed at EV Engineering put together a complete 3 spring clutch for me for a reasonable price and I added a new SRM alloy pressure plate. A world of difference, much lighter lever and I only get a false neutral if I'm being sloppy.
If the 4 spring centre is still good you can modify it to work with a 3 spring chain wheel, map make a nice 4 spring alloy pressure plate as well as the three. I use this set up with extra plates and 4 heavy springs to cope with the power of my 883 motor. So the 4 spring versions can be used to good effect when you need the extra clamping force.
I replaced everything. I ran around in circles with it for sometime,replacing the most worn out bits, but being 50 yrs. old it all had too much wear to really work as it should. A worn part has a tendency to bitch up a new part it comes in contact with. My hub center had too much wear also or I probably would have done something like Mark did.
'map make a nice 4 spring alloy pressure plate as well as the three.' as do SRM, a worthwhile investment.
It seems that these days, bet kits are similar in price to replacing complete clutches, maybe worth looking at. Some blokes used Trident clutches on 'em too. I used a 4 spring when racing, better than the 3 spring by a mile. Not just spring weight but method of construction/operation. You still can't beat Surflex plates either.