Actually, there is a difference in the MY 98 and the later heads. On the later heads, both sides have a hole for cam position sensors. MY 98 heads only have the side with the single cam sensor drilled. (I don't recall which one that is)

 

Thanks I been busy with work so I haven't had a chance to go and compare the the difference, but I will be alert of the cam sensor hole because both of mine have it.