The only concern with milling the intake is the depth of the counterbores for the alignment rings. The rings can keep the manifold from fitting snug against the gasket if they bottom out in the counterbore. You might need to deepen that cut a little with a hole saw in a drill press, or even some careful work with a carbide burr in a die grinder. The rings don't actually do any sealing- - - -they just keep the manifold aligned with the cylinder head intake ports. I like to make up three individual adapters for the intake ports from aluminum conduit and flat bar stock, and use three Keihin side draft carbs for a Harley Davidson EVO engine.

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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!