Hi,
Welcome to cnczone. I have a couple questions for you. What weighs 62 lbs, the whole machine? Just the gantry? You say you are using timing belts, is that to couple the motor to the leadscrew, or is a timing belt used to move the whole gantry?
If it's the whole gantry, with no leadscrews, you will need a gearbox on the stepper. You want to set it up so one step of the stepper moves the machine between .00025 and .0005" I would say. If you can get it setup that way, then I would think 100 oz motors will move it along at 20" just fine with the xylotex board, probably faster.
What do you plan to cut?
Eric