The next thing you can do is take off the rocker covers and you wil find GT40P in the casting as an identifier. Other than that I am not sure of any other way of picking them out of a crowd, like I said I am not sure about them to give any real heads up on them. However if you have these heads and you can get a hold of some of the GT40P matched intake manifolds and increase the size of the throttle body and EGR block and take them to 75mm, then you can get some noticeable gains in performance.