That is the right connector, it sits barely outside the harness, along the metal rail. One of the two wires coming to the connector is spliced into the bk/y wire coming from the distributor and the splice looks factory on my truck, not something added on later.
The Factory Service Manual refers to this connector in the section on ignition timing. It asks you to unplug apart the connector before timing the engine.
If I remember right, that plastic connector sits barely outside the harness, along the metal rail that holds the wire harness. It doesn't plug in anywhere or splice anywhere.
The Check Connector is in the main wiring harness, right above the distributor, about five inches above it. It is just above the oil dipstick. There are two wires going to the distributor, one of them being black/yellow stripe, going from the distributor to the rev switch. One half of this Check Connector is spliced into this wire. I have a photo of this check connector but this forum will not let me post a link to it on Photobucket. Perhaps you can search for it on Photobucket under george7941.
The terminals on this connector are the round bullet terminals, typically used by Grote for their truck lights. These terminals are larger than Weatherpack terminals. There is a translucent plastic cover over this connector.
Where is the check connector you are referring to?