Thanks for all your advice, It is a billet ally wheel with a steel friction plate so seems to meet all the requirements.
I think I'll give it a go as the engine is pretty revvy already so more lumpyness below 4K revs is not going to make much difference if I make some gains in the upper rev band. I will make sure I get it crack tested, threads helicoiled, and the whole thing balanced before use though. And as a bit of a safety measure to start with I'll retain the weedy standard clutch as a week link until I gain confidence in the ally wheel.
NiG
Theres nothing 'sneaky' about trying to stay one step ahead. Minimising the amount of guys I race against knowing exactly what I'm up to is a fine way of keeping an edge. And the rules do say 'type of material for rotating components' is free, so there.
Cheers
Andy