There are several companies out there which will customize your motor for you !
One which comes to mind is Plum Quick give them a call
and see what they will charge to customize yours for torque (not speed).
also read this link
http://www.buggiesgonewild.com/elect...ght=Plum+Quick .
If they can customize your existing motor then you should not have to change anything else out -$$$
