I'd begin by pressure testing the manifold to see how bad the leak is. It's possible it's so porous than no type of fix is going to work. Clamp some flat metal plates over the intake ports, and another one to the carburetor flange with an air hose quick-connect fitting in it. Apply about 3-5 PSI to the manifold with an air pressure regulator, and use a spritz bottle with a soap solution to spot the porosity in the casting. From there. you can decide whether to try a repair, or just scrap the thing and chalk it up to experience!
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!