What sort of advantage do you expect to get with an overdrive, compared to the setup you're running now? What is the optimum torque band of the engine you're running? Until you can answer sone basic questions about the results you expect to get from a modification, you need to do some more research about how to achieve the goals you have in mind.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!