So I bought a 25:1 worm drive transfer box, a 0.09kW 240v AC motor and a fancy switch and did it myself. AU$500 in parts.
I machined up a spacer block out of 25mm ally plate to mount the transfer box.
I had originally intended to mill a keyway in the pinion shaft, but decided it was easier to make an adapter than to disassemble the mill head.
Making the adapter was complicated by the shop telling me that the gearbox had an 8mm keyway, and providing me the stock, but the keyway actually being 5mm.
I decided to use 4140 for the adapter because I only had around 3mm wall thickness to hold the 2 grub screws (hard to see underneath in the picture). I didn't factor in how much harder 4140 is than mild steel and managed to wreck an 8mm 4 flute end mill..
This wasted some hours. I eventually brazed the key stock into the groove in the adapter and filed it to size. Neanderthal.
The hardest part was tightening the 4 Allen screws that hold the incredibly badly designed input flange to the mill body. As you can see here for the trial fitting they are not tightened.. as they are pretty much inaccessible.
Working out how to wire the single phase motor so that it could be reversible took a bit of time and some research. But it works a treat.
I just need to tidy the wiring a little (need a piece of 5 core wire) and it's done.
Thanks for the help and advice!