I got the lathe running by adding a VFD to the original 220V Ac 3P motor. But I am continuing to work on solutions to get the treadmill motor going, as I have another project coming up which will need powering.
Thanks to everyone for the help so far.
T

 

Like I said before, it looks like it will be possible to control the motor speed with an analog voltage. All of the controls functions are well shown in that manual in the link that you posted. The only real challenge will be physically locating the connections shown in the circuit diagrams. THAT PART will be tedious but not hard.