The Drivetrain mods you are talking about are going to require some custom fabrication as there are is currently no one offering such a system. The two main parts to probably pull it off are available from Golden Eagle (GEBE) I believe they sell their drivers for approx $30.00 and their driven Sheave for around $40.00 But thats just the start of what you will need. You will also need a new longer toothed belt as the GEBE belt isn't/won't be long enough to reach the driver on your frame mounted motor. Also because the belt does not come apart like a chain does getting it to clear your chain and seatstays is going to require some custom fabricated idler pulleys. Then you still need to modify the output on your motor to take the GEBE driver. There is a recent thread here from a member who put together a belt drivetrain for his occ chopper using one of the CAG motors from a pocket bike http://motorbicycling.com/f36/belt-drive-7772.html
You might find it informative. You also might contact Jim at Creative Engineering/Manic Mechanic and see if he can do the mod of switching the output driver on the motor?