The correct combination, as I think you probably already suspect really, is an R barrel + R head or SE/SP barrel + SE/SP head.

If you want to play safe, use an SE/SP "L" barrel with an R "H" head, but it's not an ideal situation and can mess up the jetting due to the low compression.

"Pitting" in the piston is generally a sign of detonation caused by either high compression or lean mixture.
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Andy.
NSR-WORLD.COM

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