Originally Posted by moparx
i think there is a cast X or J under the valve cover, somewhere close to the head casting number.
beer

Those letters are cast into the head by the spark plugs, #7 on the drivers side and #2 on the other side, the head casting number is cast on them near the 2nd rocker arm stands scope
BTW the 1970 to 1973 340/360 915 heads came in two different valve sizes as well as several different letters cast on them not just the J shruggy

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)