I suspect these are nema24 and I incorrectly called them nema28. Everything else seems to fit.

What does concern me is the points raised by some about the inertia and general mass of the screws being too much for the stepper motors. Obviously its hard to tell without testing and you can be sure I'll post some video's of the machine working to allow you to look for any issues that I might not be able to identify being a beginner.

Supposing I do find that the motors are inadequate, how big of a job would it be to upgrade them to something suitable?