I gather the present motors are DC Brushed? If they are in good condition I would tend to look at matching them up to modern DC drives like A-M-C.
AC motors and drives come up on ebay all the time, however it is a bit harder matching up AC motors and drives of different makes, unlike DC brushed which is relatively easier.
If the present motors use dc tach's, they can be disconnected when using modern drives in the torque mode.
Going this route it will not be necessary to match motors up or change mounting etc.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.