These days every head may not be pressure tested for porosity, Edelbrock included, forget about x-raying them for cracks from stress risers.
It would be unusual but it is not impossible that it is cracked or porous. When you have excluded all the obvious, what ever remains, no matter how seemingly unimportant, must in fact be the answer. (Thank you Sherlock)
I don't know which sealant is being referred to here but I believe what the sealant is doing is plugging the hole with fine particles, much like platelets do in the blood to stop bleeding.
Personally I don't like them or the posiblaty that they are going to lodge (like a blood clot) in something like the radiator core and cause it to loose efficiency. Especially in a car like a Pantera which has a marginally adequate system to say the least. But that's just me.
Pull off the head. I installed a removable panel on my bulkhead. Seems I was in your spot one to many times before?
