fattest cam in a 340?

Even if the balancer slipped you should be able to find TDC see where the timing line is(is it set to O degrees,it should be).If not mark it with a good visible marker.Set the timing from there.As for seeing it with a standard gun unless I'm forgetting something,you can't.340's like about 18 degrees initial timing which is way around from the standard marks and unseen.A good digital dial back gun or timing tape is the best way but you can find TDC and put a separate color mark at the 10 degree mark on the lower side of 0.Start it up and see if that mark is hitting around8-10 degrees on the upper side of 0 which would be 18-20 degrees initial.