[Mr70]

In short,it was originally a California only emission mandated by the Federal Government beginning with the 1970 model year,whenever a vehicle was sold BRAND new in the state of California and certain southern most areas of Nevada too.For All passenger cars & Trucks having a gross vehicle weight of 6000 lbs. or less.
If they were assembled in the state Calif,and shipped to another state,they did not have to have E.E.C.
If they were built out of state,and shipped to be sold brand new in the state of Calif.they had to have E.E.C. added on before titled.
It was designed to minimize fuel vapors that normally escape into the atmosphere from the carbs fuel bowl & fuel tank.
Not to be confused with A.I.R.aka-SMOG,or even T.C.S.,....E.E.C.was known as RPO NA-9,which consisted of many intregal parts.The most obvious being a carburetor insulated heatshield,special modified carburetor,pressure vacuum gas cap and a Charcoal filter cannister to capture unspent fuel vapors and recirculate them back into the gas tank via a rear mounted liquid vapor seperator block.The charcoal cannister,similar in size to a Coffee can,is mounted behind the drivers side headlights on a special bracket bolted to the radiator support,with 3 purge hoses running into it.
It became standard equipment on all vehicles sold in all states in the years following 1970.
That is the correct heatshield part number for the vehicles you listed.