I can't remember the application but there were a few options available with the deep neck. If I recall correctly 1 was a tractor and 1 was a foreign car that had a 7 lbs cap. If you have a good radiator ( been re- cored ) you can probably get away with more pressure than the stock cap.
The rad may take more pressure but will the heater? I usually put a lighter cap on an old car than it came with stock, to ease the pressure on the rad, heater, hoses and pumps. Packard is another car with a deep radiator neck, that takes a special cap.
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