X Heads vs J Heads

I have two sets of "J" heads and one set of "X" heads. they all came with 2.02 intake valves. They appear to be basically the same. Supposedly the "X" heads have slightly smaller combustionn chambers and will make a bit more compression. They seem to all flow about the same. You can CC a set of "J" heads and have them milled to "X" head specs easily.

I agree with the idea to use "J" heads for racing applications where you will port the heads. Save the "X" heads or restoration projects.

Bob