I happen to have a NOS motor off of a Suburban cylindrical grinding attachment for grinding punches. These motors cost about $850.00!! They have a built in variable speed unit enclosed inside the rear of the motor housing.
I have been thinking of mounting it with some rare earth magnets above the compound of my 16" lathe. The compound is large enough to mount the motor on. I could put a small pulley on the motor,and just use a vacuum cleaner round belt to go around the dial of the compound,which I'd lock so it couldn't roll freely. The first thing I have done with some new lathes,was take out the spring inside the graduated ring. They never turn freely enough to allow delicate adjustments. I drill and tap a hole,and make a little knurled knob to lock the dial with. When loosened,the dial is perfectly free to be adjusted.
Old time lathes,even into the 20th. C.,used "overhead drives". Hardinge WWI era lathes had this. You had belts hanging down that could be used to power the compound. Toolpost grinders could also me powered this way,as well as early milling attachments,etc.. The main overhead shaft was powered from the lathe itself. Angle irons could be used to make one for a lathe. Be careful to not make it so a belt could get tangled in the work,though!! That might bend the angle irons and bring the whole shebang down against the lathe. Perhaps WEAK belts would be in order,so they'd easily break if caught.
Those early methods were not OSHA approved!! Back then,you were expected to have sense enough to not get caught in gears,belts,etc.. That didn't always work out.