I was under the belief that once a lobe on a cam has wear across the whole lobe, its gone. Lifters are ground with a taper/crown. In that pic you can clearly see wear the whole way across a lobe. I think the cam is going flat. I would go back to the lifter/s and see if a tightening up quiets them down, although it sounds like you already did this once. If you have a dial indicator you could check lift off the top of a pushrod to see if its off the mark.