if the ring was made thinner round the edge you could use the flats that already on the pulley but it would mean drilling and tapping to bolt it down
im still unsure what the start point is your image vocky shows 0* and notch 5 so is that tdc on the engine is the crank sensor at notch 5 on the trigger wheel ?
EDIT: if you are searching for the correct timing marks please continue through this thread, the below image may not be accurate
