I'm in a similar situation, just that I have only the lathe. I was not impressed by Welsoft either.
I am somewhat unsure if changing the steppers will be necessary. I think I would try the ones that are there for starters. A modern chopping and microstepping driver can handle them as well as more modern motors. Using the existing ones will allow you to do your conversion without disabling the machine(s). Just unplug them from the current electronics and hook them up to your new one.