Nema 23 is a direct physical size bolt on replacement for the Emco stepper, the shaft size is 6.35mm (1/4") as Emco but may be a little shorter output shaft but you can always secure the steel output pinion with Loctite or similar retaining compound.
You will have to replace the stepper control boards to drive the new steppers, this also means replacing the control system to Mach or similar, in other words a complete retro-fit.
Quoted holding torque is about twice that of the original Emco stepper so should be OK.
If you only want to change steppers so you can use Mach or similar control system have you seen the article in the F1 group Files section by Peter detailing a low cost conversion that retains the original Emco power supply, drivers and steppers ?
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