That restricted hole might be there to route coolant flow through the steam holes better. I had a student once who was smarter than the people who made the gaskets and opened up some holes on a set of 302 Ford head gaskets. Instant overheating, and a repeat of the job!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!