I just bought a ls6 block and have a question.how do I tell what year block it is?I checked the casting number,but isn't there something different about the head bolts being different on later blocks?I need to make sure before i order my arp head studs..also,i noticed around one of the cylinder sleeves it had a slight defect in the block.almost like the aluminum didn't get fully cast.Is this something to be concerned about?Thanks,Scott