Hi Lyn,
I have a Chester 626 mill which I converted to use a 3-phase motor via an inverter. There was nothing wrong with the original set up, but I favour the flexibility and smoothness of 3-phase - I would not go back to single phase……..
I still have the original motor, which can be yours with a moderate cash adjustment. This has the great advantage of a like for like swap, but you are not improving your machine! I fitted a 1.5 HP 3-phase motor which bolted straight on and used the original pulleys. I just leave the belts on the 1000 RPM setting and adjust the motor speed as needed. I can dig out the motor spec and supplier if you like. I can’t recall it being too expensive.
The inverter came from a chap who regularly advertises on John Stevenson’s Home and Workshop site, and, I believe, on a certain auction site. He supplied a remote ‘pendant’ for ON/OFF, FWD/REV, speed, JOG and EMERG STOP, which I fitted to the front of the lid of the mill. I can supply more details if you like. Again, this was not overly expensive.
As has been said, it is your mill and your money, but I find the 3-phase set up so much better than the single-phase one; even just using an edge finder, with one twiddle of the speed knob I can set 150 RPM, then once the edge is found I can wind up to 1000 RPM for small hole drilling - in no time!
Hope that is of some use.
Best regards,
John