I took the spindle out today, not too difficult, but it is a little diferent to the G0704. Surrounding the drawbar collar is a steel collar, which seems to be integral to the gear-drive. Once the spindle was removed I had a peek down into the hole, and looks as though this collar is joined to the splined section which is driven by the gears, and in turn, drives the spindle. This should make the belt-drive conversion easy, since I can just bolt the pulley straight onto this collar.
Anyhow, there are some photos of this detail below, and a piccy of the litle light which is up beneath the head too. Unfortunatley it only worked for a few seconds then blew the bulb.
The spindle bearings required for high-speed will be two of the 7005B variety, which I cannot find in the UK so will need to order from VXB.com These are the same size as thr G0704 upper bearing.
I have measured up for the ballscrews today, so once they are drawn up, I will order from linearmotionbearings2008 on ebay. He seems to be 70% cheaper than any UK store, unless anyone can tell me otherwise!