[bigblockv6]

My understanding is all GMC V6 engines 351 through 478 came equipped with Sodium cooled valves, all 305 engines did not and my factory GMC manual confirms this, stellite is a hard alloy used on the valve faces that come in contact with the valve seat. There was an HD305E V6 that was available in pickups, my 68 was equipped as such and this engine used valve rotators.