Dude, you crazy.
I know, I can't believe I'm wasting my life like this
. My only excuse is that this spoke nipple solder to cables project is a test-run for your Resilions. Stay-Brite 8 is used as a bronze-braze substitute for low-temp or less-accessible HVAC work, and I used to use it for water bottle and dynamo mounts years ago before I got a MAPP torch. I figure it's stronger than the cast lead cable ends of yore, at least.
If I had bought a Trek 720 touring bike in 1982, it would have come with those. But alas I was a poor college student at that time and I could only afford the frame. I put Suntour Superbe brakes on it, which were fine, but I always wanted a pair of GC450''s since that's what the bike was supposed to have.
Before I found a pair of GC450's found a pair of Dia-compe 515's which are similar but different. Pretty nice, actually! Naturally, after I stopped looking for them, i found GC450's fur a good price and was happy. Until I ran into the problems you describe. I went back to the 515's, which are still on that bike.
I saw your old thread about that bike! Looks like you had some good times with it.
The NGC450b seems to be yet another instance of Trek spec'ing the weirdest and least-suitable components as OE for touring. Like helicomatic, I suppose.
I operate these NGC450b brakes with Superbe levers, which I love. Together they really do the Mafac slogan justice:
un doigt suffit (one finger is enough). The bearing mod should be doable without a lathe - you'd start with an ordinary M5 bolt, then build up the threads up to 6mm with J-B Weld or the aforementioned solder, and add a washer. Or better yet, file off all but the last 3mm of the threads on one side of a set of Nitto or VO canti rack mounting bolts and fill in those remaining 3mm of threads, and use a die to thread that filed-down post to M5, then there you have it. I bet the results would be good 'nuff. I have slackened my standards due to the pandemic closing everything down, however.