No heads have upper and lower heat crossovers. I think that you are talking about a dead hole. Filling not needed unless you are going to use a manifold gasket that doesn't cover it.
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Bill
64 GTO, tube chassis w/606" IA tall deck, PG & a pro geared Fab 9". 2750 lbs.
[email protected]/4, [email protected]/8, 1.1981-60-ft. 8/10/08
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