Help ID this Napa Echlin...thing.

It's not a relay. It appears to be a thermal sensor-switch for the heater in an aftermarket electric choke. You'll see one much like it here, but with only one wire. That one wire goes to the choke heater. The big copper mount is also a ground path; as it warms up, the thermal sensor-switch gradually decreases the resistance in the choke heater's ground leg so the heater warms up progressively more and more to relax the choke spring tension and allow the choke plate to open. The simple one-wire variety senses engine temperature via the big copper grounding strap. You mount in a location that heats up at the right pace and to the right degree to operate the choke correctly. Usually this is on or near the manifold.

Yours has more wires and appears to be more intricate than the linked one. Does one of the wires go to the engine coolant temp sender, or does it just look that way because of the angle of the photo?

It also does not appear to be hooked up any more; looks disconnected and abandoned.

I do see an electric choke on your (nonstock) carburetor. Can't see for sure, but it looks as if one of its two terminals has a wire, but the other might not. Without a thermal sensor-switch (either built in or external), an electric choke of this type will not behave properly.