It's also almost impossible to install a manifold assembly without alignment rings and avoid a vacuum leak. If you don't have the OEM rings, a piece of exhaust tubing with a slot cut into it can be trimmed to the correct length so it fits the hole in the head or manifold correctly. The slot doesn't even have to be welded- - - -it just aligns the head and manifold- - - -the gasket is what does the sealing.
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!