Seriously, I'd replace the thermostat housing, install a new gasket (unless you get the O-ring style), and use a small amount of blue RTV.
More info on what you described as the "plain tube". If I'm correct, that tube plugged into a port near the top of the 2100 carb that accessed filtered air. It's function was to supply filtered air to the heat tube air supply and to the canister. Does the Holley have such a port near the top of the carb? MD
The item you described as "the small vacuum port on the autolight " is actually the fresh air port that supplies filtered air. Look carefully and you should be able to see the port accesses the air stream above the carb , on the clean side of the air filter. MD
