decoy,

You are correct in that the 4.2 is a bored 3.8, but the 97 4.2L really hasn't had a problem with head gaskets. The problem is almost exclusively with the timing cover (i.e. front engine cover) gasket. And, in many other cases, the lower intake gasket. Just wanted to clarify because I know some people would panic and want to get their head gaskets replaced.

 

Oh s*it!!!! Now I have to worry about my head gaskets?
Nah,j/k....I knew that....wait,I better knock on some wood!

 

I do not think the 4.2L is bored out differently than the 3.8L. I always thought the displacement difference came from the stroke length. I believe the 4.2L and the 3.8L are the same bore just different strokes, resulting from the crankshaft, piston height and rod height of the 4.2L.

Definitely not an expert here but this is how I understood it. Think of the 4.2L stoker kit Morana ect... sells for the 3.8L engines.