Bravo Nexus! That truly is brilliance.
What is the shell width? Some older Italian BB shells weren’t the supposed standard of 70mm but were smaller, around 65mm. This will make things really tricky if you’re using a modern cartridge BB. In addition some shells would have been faced a few too many times making them narrower than is ideal.
This would be my 2nd guess, I still think your BB needs to be cleaned up and re-tapped but measuring the shell might be the deal breaker as a narrower than standard shell can mean it’s project over time if you have to use modern cartridge BB’s.
There are options but some items are exceedingly rare and it becomes increasingly tricky with regard clearance, chainline etc etc.
Campagnolo chorus bb is a 102mm, Iused one on my Tommasini.
Wiggle Australia | Campagnolo Chorus Double Tapered Bottom Bracket | Bottom Brackets
Like spirito said you may need to chase it in deeper.
There are a couple of other options, the old mavic bottom brackets donot use the threads in the shell, I am pretty sure VPmake something similar?
Thanks Spirito, ill have to take a closer look at the inside of the frame. I hadn’t thought about the depth of the thread, I think your on the money with this.
mitering of the tubes could also be a big one, had a similar issue.