Without finding the datasheet for the original motors, 200 oz-in = 1.4Nm.
.
The HSS57 closed loop servo will work well. Just remember you'll also need to get new couplers/pulleys, as I'd guess the shaft on the original stepper shaft will be a good bit bigger than a modern Nema 23 motor.
.
Personally, I'd avoid the integrated stepper, not because it won't work, but because you need to run the step/dir wires to the motor. If you've not got differential (line driven) step/dir signals available, it makes things very prone to noise.