2 340 questions

The "big thing"? dont know what you mean. You dont see as many mopars with them, because the cost is high, and the lifter angles are terrible, so the valvetrain is much less stable at the rpm ranges most roller cams will operate in. There can be other oiling issues too, butt hat's the main reason you dont see them. Now, you see more because the larger stroke engines really make good use of a larger cam, but at lower rpms. The X may have been machinied off when the factory drilled the spark plug holes..Wouldnt be the first time that happened.