Tom,
If that's the engine from his INDY car he told us he used gas filled "O" rings, the ring looks large for an standard copper or stainless steel .040 ring. Does the head have a reciver grove? hard to tell from the pictures? Or is the head for a double ring? If they are gas filled they may be rare, don't lose them.
Anyway seal water and oil with silicone and you should have no problems.
Harry
