Whoa! You are confusing the "coffee can" sized vacuum cannister with the Evap/Em cannister. Vacuum cannister usually located on the left fender inner apron, just in front of the firewall.
Evap/Em cannister looks totally different, is located on the right inner frame rail, usually below the alternator.
Evap/Em: Unleaded fuel,
non vented fuel cap. Originally the fuel filler tube had a restrictor in it that served two purposes.
The Evap/Em non vented fuel caps have 4 prongs on them, 2 above, 2 below 180 degrees apart. The restrictor had a provision for the 2 lower prongs.
Back then, there were two different diameters of filling station nozzles. The leaded fuel nozzle was larger in diameter, would not fit into the restricted fuel filler tube.
If you have dual fuel tanks, you have two fuel vapor valves, one in each tank, two restricted fuel filler tubes and two non vented fuel caps.
When catalytic converters were introduced, some peeps knocked the restrictors out of the tubes so they could use leaded gas that was cheaper than unleaded gas.
But guess what? They didn't realize that the lead in the gas melted the charcoal inside the converter, shoving it into the muffler.
It wasn't too long before their vehicles sounded like vacuum cleaners headin' on down the road.
And it wasn't too long before their vehicles quit along the road. Muffler plugged solid with melted charcoal.