I was never sure of the function of those rings- gland rings, as they were called in parts books at the time. I have seen them squashed, bent and missing, all without any noticable change in engine operation. The only purpose I think they served was to ensure that the intake manifold and gaskets were properly aligned with the ports on the head. That also took care of aligning the exhaust manifold.
After reflecting further on that question, I thought of a couple more functions for them: to cause grief and difficulty for anyone assembling the manfold to the head (I've had to retrieve a good many of them from under the vehicle after they fell out); and providing a topic for on-going speculation about their function. I'm sure some old-time engine designer at GM thinks this is all pretty funny.
Harvester
