That wouldn't work worth a shit. They're too small and they're designed to increase the frequency, which is pointless.
Works great, which is why everything being produced these days is inverter drive, and freq drives come in hp flavors higher than anything you'll ever own.
Increasing the frequency is not pointless, you can re-gear the machine for max torque/low speed, and still be able to turn up the machine a decent amount (limited by what the bearings will like on the drive side, I imagine) without having to fool with gearing. ALL newer welders are inverter machines, and you can ask the guys using them if they like them as they can build *any* waveform, allowing all sorts of cool shit to be accomplished.
The machine has like 30 speeds by gear plus a variable drive on the motor already.
So do you regear for everything, or use the onboard freq drive?