[ford38v8]

Bob, Your reading about the subject has not sufficiently educated you before you jumped into action. It's not the intake manifold that you block the heat risers on, it's the engine block itself, and the ideal device to block it with is a wheatstalk penny, (one on each side) as the metallurgy of that vintage penny is perfect for the job. It taps right into place in the block and stays put. Nowadays, the consensus seems to favor the drilling of a ⅛" hole in each of those pennies, to allow a trickle of heat through. I hope that whatever damage has been done to the manifold can be repaired, and that an unmodified gasket can correct the leaky situation.