Hello,
I had the same sort of problem on my 66. Multiple bleedings, nothing worked. I tried the trick where you detach the clutch slave spring, and jiggle the clutch slave lever back and forth (firmly) between the 'stops' several times. After I reattached the spring all was well. From a post here (someplace) they said that there was a spot in the slave where a bubble could accumulate, and this moved the bubble out into the system. Easy and very fast to try.
Good luck -- Roger