Doh, thanks Matt - never occured to me that the "W" might be Watts! - didn't think anyone would even try to use a 1/3 HP motor to run a mill!!!
Looks like I need to go find a bigger motor then - the original was 0.5 to 0.75 three phase so had a lot more torque. Will probably look for a 1hp single and see if that will have the grunt to get the higher gears up an running