DA1502F is the part number for that half of the case. Looking at the diagram it appears the pulley is a push fit on the shaft, it may be a case of supporting the pulley, applying heat gently and then pressing it off the shaft. You will not be able to remove the key with the pulley on. I will see if I can get to my Barford Atom 15 buried in the shed and if it is an early one see if I can see how the pulley is held on.