I got a dimmer switch that will work:
Cast Iron, weighs about 12 pounds. Rated for 860 wats.
But you gotta be willing to pay antique rates, and shipping.

Unless it's an antique frequency drive, it's not going to work either.

Rebuilding the transmission so you can move the belt easily will
be cheaper.

Or steal the foot-pedal from someone's sewing machine.

Which would only work if it had a brush type "universal" motor - which is
highly unlikely.