Yep, on the money... my middle daughter is very arty/crafty and she supplied the extra pair of hands and the white acrylic paint and tiny brush.
Sitting on the bike, I got the throttle and top half of the switch-block in position, and she dabbed some white paint on the locating pin on the bottom half of the switch-block, and then pressed it into place... voila, marking out perfection. Chuck the bars in my vice, centre punch the paint mark, drill, then replicate that same position on the left side, centre punch and drill.
They fitted up perfectly.
I have to wait for the glue to go off for the left hand heated grip, before I can try the new bars out... but they feel ace just sitting on the bike.