The work.
It appears that using the VW thrust bearing with the Subaru clutch plate has resulted in there being inadequate bearing on the thrust plate for the clutch fingers, this has allowed the thrust bearing to go through the centre or at least be gripped by the fingers which have then spun the thrust bearing of its lever arm.
more info and photos later. Work continues to solve this problem.
Outcome.
So far the modification seme to be working well.
see (Modified dual-mass clutch & thrust bearing).