Wozza,
The pressure plate on the 6 spring clutch will slip down the centre as far as you want.
It seems to be a bit of a problem with new friction plates being too thick. I just found this with a set for the plunger type 6 spring clutch.
I have 2 new sets, one fits well, the other doesn't.
I spoke to the dealer who imports the thicker plates and was told that most people leave a pair of plates out until the fitted plates wear down then put the missing plates in.
I will probably set these things up on the lathe and skim them a bit.
Trev.