Hoss- I noticed on your G0704 Projects page, in discussing motor options, you listed a VFD / 3 phase motor option, and mentioned that the motor was quite large (56C frame, with mounting bolts on a 5+" bolt circle) and that you were looking for a smaller motor option. There is a 3/4 hp 3 phase motor on surplus center right now that appears to be quite a bit smaller- it says it has an 85mm bolt circle on the mount, and the shippinng weight is only 16 pounds. Looks like it would fit on the belt drive mount. Price is right too. I assume you would use the same VFD (next size down is 0.5HP). It's a 3400 RPM Motor, but with the high speed pulleys on the belt drive, you would still get respectable speed. Also, the 3400 rpm is at 60 HZ, and the vfd's generally have the capability to go up to 100 HZ. Perhaps you could get more rpm by overspeeding the motor a bit?
Surplus Center - 3/4 HP 3400 RPM 230/460 VAC 3 PH MOTOR