[Al_The_Man]

The motors shown are 6Nm which is equivalent to 850 oz-inch. 2000 rpm max
If you go with a brushed servo you could use the 6Nm figure but remember that AC servo's usually have less inertia so you might want to go to a bit larger if you want the same speed as previously, those robots can really move. Worse case senario is that you may have to drop the acceleration if undersized, there is the usual limitations with steppers once you get up to the high revs.
Al