If you look at the center picture (post #5) you will see a cast passage directly below the Valve Cover lower edge. There is also a cast adaptor mounting plate on the front of the heads.
I believe the air went into the adaptor plate, traveled thru a cast in void, exited the plate into the open cast passage, and then traveled down that passage with air being introduced in each of the drilled passages going to the exhaust ports (shown in the same picture). The passage was plugged at the top surface after it was drilled from the feed passage to the exhaust port.
Tom V.
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"Engineers do stuff for reasons" Tom Vaught
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