After some thought, I decided to just go ahead and get a torque converter. A torque converter is nothing but a varable speed transmission that changes a belt position from two pulleys. Low engine speed results in better pulling power than a clutch, and changes to a lower gear ratio as speed increases. This is a Comet Torq-A-Verter I got from GoKartSupply.com (a local company for me, so I was able to pick it up directly). The nice thing about this cool setup is it is self contained. Instead of the jackshaft setup Manco supplied that mounts under the engine, this has it built into the main plate.