BAZINGA!! why would the the oil passage that is blocked with magnum heads have rust in the passage?? (I thought it was water passage at first)

I think the head gasket might be the problem here.. maybe both.

you have the LA head gasket with the open hole for LA style oiling to rockers and a magnum head gasket does not have the hole punched.

the oi pressure might have started a leak to the water passage and on a shut down would then let water into oil passage.

look at the gasket real close around the LA oil passage to the rockers, which is rust coated as far as i can see down inside.

do you have oil in the rad or coolent system?