I have a 2000 xj that I am chasing down problems on. I have the cylinder head off. Wondering how can I tell if the head has been replaced? I am not finding a crack between 3 and 4 but the head gasket was blown between 5 and 6. Just wondering if there are any identifying marks that would designate the newer updated head? Do all the updated heads have TUPY stamped on them? or were there other heads that were made that were reinforcied in the critical area that are NOT marked TUPY?