Some 50 years ago, I had a M18, used for fun-racing. We welded up the cams, and grind them down acording to a cardboard profile one of the guys had gotten hold on, to increase the lift an duration. And we added an extra valvespring, as I recall it, an echaustspring from a Volkswagen 1200, placed under the original hairpinsprings. And then a bigger carburetter. Wow, did it go! What a lot of fun we had, for very litle money. I realy loved that bike, we spend many good times together.
I have a 59 model so not sure if the cams are different but on mine you alone the dots the same way as you did but also go by the number on the dot as there marked for different tuning one being 350cc and the other competition. My 500 single is on mark 1 exhaust side and mark 2 on the inlet side as suggested in the Ajs matchless Service manual by F NEILL
Time the 500 as the 350, per Ken de Groome's article. In addition , change the inlet pushrod rocker arm for one from the 250/350 lightweight model. Makes quite a difference.😊
