The block says 10-72.They are definitely 346 heads with the peanut plugs.I will try to get a pic of the unusual head gasket.Does anyone make the correct head gasket for the extra cooling heads.
10-72 is a casting date that would make it a 73 model year engine ...
Picture of the heads with plugs in and out and the head off the engine would be nice.
Felpro 8519 , the standard gasket in their kits , has the holes but it's double the thickness of the steel shim originally installed in that motor so it will be a slight compression drop.