X-heads vs J-heads: what's the difference??

I'm inclined to agree with RRR on this but I'll say it is regional. In the late '90's around here, I couldn't hardly find either, which makes the price go up quite a bit!

I'll roll Magnum heads, cracked seats and all, if I'm going to run used cast iron. EQ for new cast iron, Aluminum if I get rich anytime soon.