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The phone signal and base power are low voltage so the two lines coming out of the same plate at the phone is not a problem, but the wall wart power going back under the outlet cover plate could, depending on how picky the inspector is. But there are combo low/high (120 volt) boxes. Then have the 120 outlet in the high voltage side of the box, and have the wall wart output (going to phone) go back inside the low voltage half of the box. Retired EE.
Look at soundown.com for foam/lead sandwich sound deadening sheets. Worked well on boats when I was in the marine industry. Also has lots of general info on sound control.
Nice. I see some comments like how 'bout pliers, or go buy an adjustable. Using the right tool is always the best choice, but sometimes you are out in the Maine woods on a Sunday afternoon with a 5 mile hike and a 50 mile drive to a hardware store. A good craftsman can make a tool or part from materials available and get the job done. I still have some tools my Grandfather made. Can't even find tools like some of them today. Cheers from "Mr. Wizard". Bangor Maine