Other than maintaining the original appearance, is a 3-bolt flange the only option? How about fabricating a 4 bolt flange from 1/2" or maybe 5/8" steel plate, and weldng it onto the original manifold after milling the broken flange off? Then make an identical shaped flange for the exhaust pipe. It would also be possible to fabricate some sort of support bracket to keep the weight of the exhaust pipe off the new flange to minimize the strain on it.
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!
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