As the X2 mill is frequently converted to CNC with at least acceptable results surely simply slecting a motor of at least similar, preferably greater, torque than the preferred size of stepper motor would be effective.
Going all round Robin Hoods Barn to get measurements of a torque hopefully somewhat equivalent to that needed to drive the mill table under respectable cut conditions then searching for a motor of useable size whose specifications are acceptably close to the measurements seems to involve far too much faff and wasted time.
Personally I'd just copy a known to work CNC conversion stepper motor set up, hook the stepper driver up to a simple variable pulse rate generator for speed control and call it "Job Done". Initial prices might look more expensive than ferreting around but you get it all in one hit and know exactly what you will spend. Leaving aside the time invested in finding and making which could be better spent on what you really want to do ferreting around always seems to involve extra costs for odd bits'n bobs that sorta got overlooked in the initial planning stage. Its easy to spend almost as much, often more, on an OK(ish) DIY contraption than buying properly sorted commercial kit.
This old fogey in particular has a hard job keeping up with how relatively inexpensive quite sophisticated components and gadgetry are these days when compared to the 1970's when he first started taking notice!
Clive.