FWIW,
I have a similar machine to the WM290 which originally came with a dc drive.
I changed the motor to a 2 pole 2800rpm 1.1kw 3 phase motor in an 80 frame size, it occupies the same space as vacated by the dc motor.
I used an Invertek vfd and set the max frequency to approx 72 Hz to give me the same spindle speeds as before.
I had no need to change belts or pulleys.
I used the existing speed control pot, rewired the FWD/REV switch to give the desired functionality for the vfd.
No additional switches or buttons.