I use a socket that's a snug slip fit into the manifold passage (not the counterbore) and use it as a forming jig to make my own alignment rings. A diagonal slot isn't a problem, since the rings don't have to seal vacuum- - - - -they're just for manifold/head alignment.
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!