Also check the metal clamp holding the distributor in place. I once had similar symptoms, stuck on the road not far from home, and it took the RACV (similar to RAA) mechanic an hour of frustration until he tracked it to the broken clamp which allowed the dizzy to rotate freely at will.Check the distributer cap is not tracking/cracked between two adjacent plug leads. Seen that a few times, usually on the inside, in the early days. Engine can then try to fire at same time on opposite banks, giving a backfire, knocking and all sorts of other effects