Hello, thought this would be of use to someone here, who's thinking of fabricating their own lockup clutch. These drawrings are in autocad and for a gsx-r motor, but can be easily adapted. Bear in mind you have to extend the clutch housing casting somehow to allow clearance for the lockup arms to throw out.
Why a lockup clutch? well, because you can still run nice soft clutch springs that slips easily low down, but when the power really comes in midrange, the lockup clutch pack forces the plates together harder with centrafugal force. So no slippage when your nitrous/cams/turbo/supercharger comes in (delete as appropriate ;p ) .
http://www.turbomoto.com/lockupclutch/
The zip contains all the files in a zip archive...

interesting......