Reporting back as it may help others. I got up the courage and went at it, slow and careful using the brushes in the image above and a spray of cutting oil on the brushes and inside, worked a treat, threads are fine, the shell is as clean and shiny as the day it left the builder, or maybe better. I first tried the 28mm brush, slow and easy, not too much back and forth, checking after a few turns, checking that the cups still went in, wipe, and repeated. Then I got extra bold and forced in the 38mm brush worried it might not turn but it was fine, again a few quick turns at slow speed, worked from both sides not pushing it back and forth all the way through just to be safe, and the shell was left pristine.

Sadly, the drive side threads were cross threaded from some previous owner, I was hoping it was just gunk and rust, the facing is pretty raw too, looks like a hack with a file, now I know why I got the frame cheap. Now I need to find a shop with the tapping tool and the facing tool too. needs a headset pressed in and maybe the fork cut down a bit, could use a repaint, lots of serious flaking around the BB and the headtube that Moser diligently chromed and then painted over. Maybe there's a proper prep for chrome but they didn't do it.

I'm in a provincial part of Italy and tragically all the shops with such experience long closed up, only shops around me are "youngsters" with mostly carbon fiber press-fit experience, I know more than them regarding steel and just don't trust them even if they had the tools. This bike needs the fork cut down too, I'll probably have to ship it off to someone, somewhere, my cheap race commuter risks becoming my expensive race commuter.