I've used a tiny drop of glue, like Doc said, and finished the build.
The amp started right up, and sounds well too!
The purple glow inside the 0D3 is just barely visible in the picture, but it looks fascinating in real:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FdmIx3TD.jpg&hash=04e8b494ec6f88913389a6ad34cdb7d247abab55)
Thanks again for your support!