The main cause of such gasket failures is detonation. Anything over 9.5 or 10 to 1 is too high for pump gas. If you have 11.0 to 1 you will keep having troubles. A band aid fix is to retard your timing to 32 degrees total. Also on the old engines the vacuum advance was on 'ported' vacuum instead of constant vacuum at idle. Ported vacuum has no advance at idle and high advance the higher the engine is revved. So if you were hauling down the freeway you would have maximum advance and were probably detonating.Sort out your timing before you hit the gas again.
Perry.
