Z 900 - Alternative gearbox

I race a 1975 Z900 which has been quite extensively modified. I still have the original gearbox fitted to the bike. I have tried Nova Racing in the UK, but they have never built a close ratio box for a Z900. I have heard that a GPZ Ninja 900 box can be used with minor modifications. Could someone perhaps point me in the right direction.

Gos??

CALLING GOSLING!!!!!!??

he will be here shortly no doubt..