why J heads, why not x heads?????

The X heads are only better if you just want to say you have X heads. For all practical purposes the Js and Xs head are the same except some Js had the smaller 1.88 intake which can easily be machines for 2.02. The Js with 1.88 are the exact same casting as the Js with 2.02 except they are machined differently for the respective valves after they were cast. Same goes for the TA and AAR six pack J heads, same casting, just machined differently.