Hi Spooky:
If the little device you have circled has at least one hose back to the ECS vapor canister, then it probably is a thermal delay valve for the ECS. The thermal delay valve prevented ECS vapor canister purging until the engine was warm. There was quite a few changes in the design of the GM ECS system for your vintage truck, but I am sure that little device is a ECS control valve. If the connection to the carb is gone, you would want to re-connect it or at least make sure the carb end of the connection is plugged so the carb doesnt have a vacuum leak.
Regards,
Henry