I highly recomend one of transmission specialties spragless race converters, they are virtually indestuctable.
They can custom build you one for your application, just call them up and tell them your specs and they will get the perfect converter for your set-up, also they offer a free re-tweak if needed within 90 days of purchase.
Here's a link to their site.
http://www.transmission-specialties....hp?cPath=23_43