Lancia Motor Club

The clutch on Sheila (my VIIth torpedo from Oz) recently gave out.  On examination I found that only two and a half Ferodo plates had been engaging in the basket and the rearmost had stripped its teeth.  As I also had the box and clutch out of Boot I was able to compare the two.   
The dimensions and distances of the clutch plates vs the gearbox appeared the same but the engagement of the clutch into the basket was different on the two cars.  Presumably, during its restoration, Sheila had been fitted with new engine bearer tubes with the holes in slightly different positions?  However, when I tried to move the gearbox forwards to engage the clutch plates fully in the basket I found it was obstructed by the clutch retaining nut (Consortium, 17mm thick).  On advice from John Vessey I reduced this to 13mm thick - but does anybody have a Lancia nut to determine the correct thickness?   I then fitted a new back plate and an extra intermediate (driven) plate next to it to push the  Ferodo plates properly into the basket and it all works sweetly.   What a lot of fiddling and fettling.  The clutch had always tended to slip before and I had blamed the Consortium spring )I also fitted an original square section spring from the bits box) but I think the incorrect engagement of the clutch into the basket was really the problem.