Want to swap the single phase 0,75kW/1HP motor in my MD-30 mill for a 3 phase one so I can use the inverter I bought.

The current motor has a 19.8mm shaft (as best as I can measure without taking it out), a footprint of ~ 140 x 105mm and a centre to base height (I assume thats measured to the bottom of the foot) of ~90mm. The latter two measurements suggest this is a 90S frame motor, yet the 0.75Kw rating and the 19mm shaft confusingly suggest a 80 frame. The motor casing is 275mm long, which also suggests an 80 frame (90 frame being 325mm as far as I can make out). Most 1hp motors come as a 80 frame except 6pole which are a 90S frame, but this is a 4 pole motor.

All the .75kw/1HP motors on eBay seem to be 80 frame. I suppose I could get a chunk of 10mm aluminium plate to make an adaptor but this seems an expensive option on top of the motor. Or have I got a strange motor somehow.

Anybody else (Bill?) with a similar machine (RF-30, etc.) shed any light on this?