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

Many of the 1.88 intake J heads tended to be porous. Hughes won't do anything except a stage one port on a J head. I ported my Jheads backi in the late nineties abd has to replace one of the heads because of pourocity in the intake. The only cast iron head I would buy is an aftermarket but, I would only buy aluminum now.