Remove the intake manifold and all the pushrods. Fabricate a flange which will allow you to apply a vacuum to the intake ports. When you find which one of the intake ports will not hold a vacuum, remove the head and find where it's cracked.

If the engine was mine, I'd use that 2-carb manifold as a big paperweight.
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!