X-heads or J-heads on a 360 LA Engine

As cast, the "J" heads (casting #3418915, a.k.a. 915--can also marked I, O, U, or Z instead of J) are actually a scosche better than "X" (894) heads on the intake side, and noticeably better on the exhaust.

As a rule, X heads are 1968-'69 only. 1970-'72s came with J heads. Some very-early '70 340s might have come with X heads, but I've yet to seen a documented, one-owner, known unmolested 1970 model built with them. I've had a few '70 340s over the years and they all had J heads except one. It was "built" and had W2s (still does).

I think I have eight of the 915s (including a pair marked "Z") and two sets of 894s. One set of the Xs has been ground through the pushrod holes, the other was from my best friend's 'Cuda from high school. I hold onto 'em for possible future stuff; none are in use at the moment.