Your '04 has the later, upgraded 3.8L with different heads. Looking at exhaust manifold gaskets on rockauto.com, the '04 3.8 gaskets are not the same as the '95 3.8SC gaskets. Whether one could make the two play together, I don't know - can't tell from the pics of the gaskets whether the bolt patterns are the same and it's just that the ports are shaped differently (round vs somewhat D-shaped) or what. Maybe just buy a manifold gasket for the '04 and see how it lines up with the '95 heads?I do have a question on the headers from the stocker n/a 3.8. Are they sufficient for the SC 3.8, will they even bolt up to the SC heads? Or should I go aftermarket?
I would imagine the 3.8SC would benefit from improved headers, and there are aftermarket headers available for the V6s, so depending on how the gasket test fit looks, maybe you could get some New Edge V6 headers and bolt them up to the '95 heads.