If you haven't heard this before, adding a variable speed drive to a lathe or mill is the single most significant improvement you can make.
Industrial duty C-face motors seem to be commonly available from many sources where HSMs look for goodies.. eBay, salvage yards, flea markets, surplus dealers etc. These motors are generally very expensive to buy new, but used/salvage or surplus prices are very reasonable, often too cheap to pass up. I discovered this 90V PM 1.5 HP Indiana General motor at a salvage yard for $10. The yard guy thought it was 3 phase, and not worth much. It had a worm gearhead on it, also in very good condition.
Here is the adaptation I implemented for side-mounting a C-face motor
WB