Take the cover plate off the top of the headstock, undo the layshaft bearing blocks from the aluminium frame. Slide the layshaft out of the belt - do not undo the belt.
pull the belt up through the headstock and remove a link from the top- it may be two with that ammount of slack.
Pull the belt down and thread the layshaft through - do not forget the endles V belt too - put the belts on the pulleys.
lever the bearing blocks onto the frame work , spin the headshaft to check.
put the bolts back into the bearing blocks and tighten up, adjust tension of lower belt.
I find doing it this way a lot easier than struggling with the belt in the cabinet.
pull the belt up through the headstock and remove a link from the top- it may be two with that ammount of slack.
Pull the belt down and thread the layshaft through - do not forget the endles V belt too - put the belts on the pulleys.
lever the bearing blocks onto the frame work , spin the headshaft to check.
put the bolts back into the bearing blocks and tighten up, adjust tension of lower belt.
I find doing it this way a lot easier than struggling with the belt in the cabinet.