My bet is that it's the head gasket. You will need to pull the intake and replace that gasket anyway when you replace the head gasket, so both will be new after you do the job. I would just count on replacing the head gasket, and I would do both heads.
Rev
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'66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi.
O.B.C. #2
'66 coupe
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