Many thanks for all the replies, the belts do indeed come off in the way described above, the motor can be loosened and tilted, then the centre pullies can also be loosened and tilted. Problem is all the heavy wiring goes through the gap the motor tilts into and this makes in very very difficult. It can't be how it was designed!
But oddly, the belt from the motor to the idler (centre pulleys, does it have a better name?) only fits in the position as shown above, for any of the other 3 positions a shorter belt will be needed, seems odd, I thought the belt would fit all positions like the belt from the idler to the chuck does (and all other such systems as I have seen in the past)
Anyway, had the machine running today and turned a bit of steel, seemed to be all working well apart from the low turning speed