[Floyd]

I doubt corrosion has any thing to do with it since we are not talking aluminum heads. The original problem is probably a result of "the last guy" in there decided to chase- cleanup-retap the threads in the block. this always makes them crooked and the studs will become a locking device when installed and torqued. An engine that has never been messed with and rebuilt without screwing up the threads will enjoy dropping the heads on without interference. They will also lift off without problems. The original Ford thread in the block cannot be duplicated and should not be touched except with a wire brush.
Been there, seen it.
My experience