summit lathe conversion

I am possibly going to be converting a manual summit 20"x 120" x 4.125" bore lathe soon but have some important questions before I begin.

This lathe has a 7.5 hp 3 phase motor an I really need to be able to keep this motor to make the project viable to my boss. This lathe is used to make new hydraulic rods daily and threading is the most important thing we do with it. If I add an encoder to the spindle can I drive the 3phase motor as a servo with a VFD or am I limited to just relying on a single tach pulse once per revolution?
If I cant do this with mach and an ethernet smooth stepper would a csmio board make it possible?

Thanks.
Marvin

Mach only uses a single pulse ,and it works well ! as you are only single point threading a cyl shaft should be no problem .
Use a proximity switch with a metal target or a gear tooth sensor from honey well .