Merv,
Where are you? In NSW, call Richard at
PR Technology (02 99056316) - he's done quite a few. But....
What is your application? Twin Plug arrangements work best with quite high compression ratios (i.e. >10:1) and high-domed pistons. If you don't have this it's probably not worth the $$$. Then you will have to engineer some sort of 12-plug dizzy with all the attendant drama - more $$$.
Cheers,
Mark Lamberton
Sydney.