There were 5 generations of head castings, and you can tell which you have by looking at the back of the head. It is rumored that the 1's and 2's weren't as good as the later ones, with the 5 being the one to use if you had a choice.

Just for clarification: There are more than 5 castings of these heads, they just restarted the numbering after 5. The heads that seem to have issues are the early 1's and 2's. That means, if you have a 1 or 2 from an 88-89 engine, you run the risk at having some inherant casting related issue.

Then again, I would not be suprised if most of these heads have already self destructed after 17 years and they are just not around in any signifigant numbers anymore.

Michael