Ford's FE Iron Heads have a 5/16" hole coming up to and thru the head. Ford would restrict down to 3/16" with the use of steel shim head gaskets also I believe Edelbrock Aluminum heads only have a 3/16" hole coming thru the head. so restricting is really nothing new.
Also, there is a well put together article in the in the FE Forums FAQ site that should cover everything discussed here.
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