I had expected slotting the nut to be harder and more time consuming than it was. This is one of those jobs that people recommend trying on a worthless guitar and while there certainly is scope to mess it up I don't think it's anywhere as dangerous as you'd expect.
Anyway the Columbus fit the bill and the new nut was grossly high so it had to be done.
The recommended method seems to be to stick something to the fretboard to protect it and guide the height you file to. I used a bit of old motorcycle inner tube.
Getting down to a suitable height proved pretty straightforward and the files cut cleanly down without wandering. Once I'd got down to the chosen level I played the guitar a little and decided it needed lowering further still. For the second cut I used a cable tie taped to the fretboard.
The guitar has very small frets which feel like those on a 70s Gibson 'fretless wonder' I once played and I've taken the nut down really low to match this. Maybe a bit too far although it doesn't actually buzz on the open strings. Still I like guitars where the nut height has been lowered beyond than the usual conservatively high default.
With the slots cut I took a palm sander carefully to the top of the nut and shaped it into something that doesn't look ridiculous. Which was also fairly easy and I'm pleased with the results. It doesn't really look any less tidy than the nut I paid a professional to fit.
With this done I gave the frets a quick polish using wire wool too, gotta polish that turd.
Finally getting to play it properly for a bit I wound the volume up on my HT1-R and found it suffered badly from microphonic pickups. Which was hardly a surprise. So I whipped my pot of wax out, melted it and potted the pickups.
I wanted to avoid taking the guitar completely to bits and disturbing the electrics so I dangled the whole guitar over a shallow container full of wax to pot them. Once cooled and with the guitar back together it's really helped, they're not 100% immune but they are now much much better.