I have dealt with old '61-'63 sd heads over the years and on one set of 980s someone had drilled a hole in the water jacket of the dual center exhaust on both sides and tapped them. I have no way of knowing if they had been NASCAR heads or drag race but the only reason they would have done this IMO would have been to install a heater hose pipe in that location on both sides to get the heat out more rapidly. Additionally I've had several sd dual quad intakes with additional threaded holes on the rear flanges both sides which too would have been to screw heater hose pipes in so heat could be more readily removed from the back of the engines/heads. These same tricks could be done on any Pontiac head. How efficient this was I haven't a clue.
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