Ed,
I have two Blue Heads, one with and one without the baffle. The one with will turn a 11-7 prop at about 12,000 RPM the one without will turn it at about 13,000. Don't remember which props or fuel. The one without the baffle is STS ported, the one with is without PDP which I think was also available on this engine. Both need an idle bar plug.

That ole Blue head came out in the early 70's and production stopped around the early 80's. At one time you could buy them in three flavors, plain loop ported, PDP, and ABC STS ported. Probably a few other changes in the decade or so they were made.