UPDATE: finally I found the perfekt solution! This clutch (CENTERFORCE DF021057S Dual Friction Disc/Pressure Plate Set) I bought from a member here on Ebay works perfectly. It fits the aluminium flywheel (MCL 563200 1964-9 5 SBF) with 8mm bolts. I had to fabricate 3 centering pins but otherwise just a bolt on.
The throw out bearing (MCL16525) also works. The setup does not need a long throw master cylinder. With the short throw there is enough travel for the clutch to disengage.
The pedal effort is almost nothing - as if there is no clutch at all. And the best thing: the clutch shudder is gone, total smooth engagement! So much more fun to drive!
Eugen