Square four Mk2 valve collett

[Andyozz]

Gents..... HELP..
I have never seen this before but the damn thing has now managed to throw a new problem at me... one of the valve colletts broke in 2 and dropped a valve. this then dislodged the valve guide which will need to be replaced along with piston. however, i am in desperation to locate a new valve collett.

Drags no longer stock them so out of desperation i am asking..... a long shot i know if anyone would have a pair or just one valve collets they would be prepared to part with..... Part number is 640-55. OR details on materials and heat treatment of the colletts so i can make one

As a side point does anyone know who supplies oversize valve guides?

Thanks all in advance.... Regards Andy