Don't go too small on the converter diameter. You'll get a "false neutral" until the engine revs up, and then you'll squeal the tires or stall the engine every time you launch. Unles you've got a very radical camshaft that needs to have some RPM built up to get into its torque band, a converter stall speed of 2,000-2,200 RPM should work well. Stock converters usually stall at 1,500 RPM or less which might not let your cam build enough torque for a good hole shot.
"Stall speed" is the point where the engine cannot accelerate any further at full throttle with the brakes locked down due to the converter developing a hydraulic lock. No matter how much torque is applied, the engine simply cannot increase speed. Somedthing will break first. If you pick a converter with too high a stall speed, you've got a race-only setup, unsuitable for street use.
Jerry
