Graham,
As Brian says, the belts are all the same length. To line up the pulleys slack off the grub screws on the countershaft cone pulley and slide it whichever way to line up with the headstock cone pulley, using Brian's ruler as a straight edge on the end faces of the cone pulleys.
The grub screws are in the 'V's of the pulley, so you will have to move the belt out of the way to find them. They only serve to locate the pulley laterally on the shaft, the drive strain is taken by a Woodruff key inside the pulley cone, so don't overtighten them.
When you have sorted out your belts, check all pulleys are tight on their shafts and your noise may have gone.