Yep. It's just the gasket, and it's my fault.
I used FelPro 8523PT1 gaskets, which are $15 gaskets.
The notes on the gasket say "OEM stock replacement Fel-Pro head gaskets are ideal for stock rebuilds on street-driven cars and trucks. Available Fel-Pro head gaskets feature both multi-layer steel-core and composition construction. Fel-Pro head gaskets are not intended for race applications."
I bought the gaskets before I really knew what kind of engine I was building, and I really didn't think about it. What I needed was something like the JE Pistons recommended GM1009-039 gaskets, which are $100 each.
I'm trying to decide whether or not to upgrade to aluminum heads. I've had a really hard time keeping this engine happy with the iron heads. It's only money, right?
A little in the lifter valley, and a little in cylinder number 4. It was starting to get into number 8 too.
I'm saying no to the aluminum heads. I'm making an adjustment with the proper head gaskets, and bumping up the cam a little bit, with matching lifters, pushrods and valve springs. That's well over $1000 right there.
Bummer.