350 head gasket

Hi All, I put a new 350 crate engine in my S-10 and have been having a ball with it, until now. The fan belt that drives the water pump departed and left me with an overheated engine. Once it cooled I filled it with water and started it up and discovered the cloud of smoke/steam coming out the exhaust and knew the head gaskets were shot. I pulled the heads and looked at the stock gaskets and I saw what appears to be a plastic coating on the surfaces of the gasket. I think the overheated engine melted this plastic and the gasket failed. Am I right in thinking the coating is plastic, something like teflon? If this is so, I guess that whenever these engines are overheated, for any reason, the heads will need to be pulled because the heat will have destroyed the head gaskets. What are your thoughts. Rick