Quadrajet question - broken vacuum port?

[mjewett]

First-time poster here, thanks in advance for the patience and thanks for help with problems past - this forum has been a great resource.

For what it's worth, subject vehicle is a 1971 GMC K1500, 350/TH350 - "restored" (by an engine machinist/hot rodder for his wife as a DD) several years ago and purchased by me ("idiot") two years ago as a "cheap daily field truck". Obviously, my wrenching knowledge is limited and self-taught, so please bear with me as I attempt to make sense out of somebody else's project. Now the issue at hand:

I'm currently running a Rochester Q-jet that a local carb guy built and tuned for me last year to replace the gas-sucking Holley I had before (best money spent on it so far). I noticed a slight hissing/squealing sound the other day coming from the carb area and a stumble at idle. While digging around for an intake or vacuum leak, I found a small hollow metal rod with a rubber cap on the pass side valve cover. Looking up at the pass side of the carb, there's a correctly-sized hole just under the choke-pull off. When I put the metal piece there, the noise goes away and the truck seems to run fine, but looks like metal piece was once one and the same with the carb body. The thing will stay in place while running in park and on a short, gentle test drive around the local 'hood (assuming this is full vacuum), but then I do bounce this thing around in the dirt pretty good for work, and it obviously fell out to begin with. Question(s):

1. Is this port intended for the thermo-valve that would have been in the stock air cleaner snout - that's what I've come up with after browsing some pics on the interwebs?

2. Any ideas on what to plug this with? Or how to re-attach this thing?

If there's any other info needed or if a picture would help, let me know and I'll add it. Any help would be much appreciated by the idiot behind the keyboard.