I have a converter box bought many years ago from wholesale tool. It has worked fine. The VFD are now around and priced pretty good. Very nice to have that speed selection. They are kind of slow to react when turning on and off.
Used an old 3 phase motor to power the mill before got the converter box.
Just get the motor spinning flip on the power then power up the 3 phase. I just put a pulley on it and used a pull rope wrapped around it.