Any question answered...

10.4 mm, I think.

MacCulloch & Wallis have what you are looking for.

This is correct

I bought this BB (because I think it has replaceable bearings). Because of fucking Shimano and their anti-standards it needs a different external BB tool to the one that everyone in the world already has. Shimano give you a piece of shit plastic one but it cams out at like 1Nm because it's made of fucking plastic. Said piece of plastic shit is Shimano TL-FC24 which in turn is compatible with "Dura-Ace SM-BB9000 and BB-R9100, XTR SM-BB93".

Does anyone know if this this Unior 1608 will work?

Where are you based - if it's what I think it is and sizewise compatible with the latest (smaller) Ultegra ones, I do have the metal tool for installing, in N8

This is what I have: Shimano TL-FC37 HollowTech II BBR60 bottom bracket socket

BBR60

There's an even smaller Ultegra now for BB9000 et al. BBR60 is the middle of the three sizes. The 1608 tool above looks like it's for the middle size too.

Ah, that is annoying then!

I'm up in Scotland but thanks for the offer!

I reckon this is what I want

https://www.wiggle.co.uk/lifeline-pro-bb-removal-tool-1639-xtr

Sure, i understand how DRM works and my assumption was that the free ebook would still be to the purchasers account and protected in line with industry standards etc...

If I wanted to drill some very precisely threaded holes into a sheet of magnetic metal measuring 5mm * 80mm * 450mm and get it maybe powder coated or otherwise looking tidy is there someone/where who could do this? How much would I be looking at?

some very precisely threaded holes

How many? How precisely?

Yes.

Don't have a design in mind yet but top of head - 20 x 3/8-16 thread and 10 x 1/4 20

Precisely enough that if I screw a spigot in it stays in firmly / doesn't damage the spigot or the plate?

I've seen this which is similar but not the right size and doesn't need the thread in the side profile at the end - 3D printed, too, so I have doubts about longevity. https://www.lsdigi.com/products/3-8-16-accessory-cheeseplate

I'd probably go to a fabricator rather than a machinist, mostly because you're more likely to get powder coat as part of the service and they can easily meet the accuracy required.

Thanks - any recommendations of where to try beyond Google? And is powder coating the right thing or some kind of galvanising or something? My metallurgy knowledge letting me down here. I guess this is what I'm trying to emulate / what it'll sit next to:

https://www.inovativ.com/shop/digisystem/components/digiplate-pro/

I want to mount it to the inside lid of a pelicase so I can fix stuff to it.

magnetic

Why magnetic? Aluminium (per your example) is a better choice unless you're attaching things with magnets.

I'd like to attach things with magnets : )

Not essential but a useful bonus to stick these on without needing extra cumbersome rigging:
https://cvp.com/product/aputure-mc-rgbww-light

any recommendations

https://www.lfgss.com/comments/15116012/incontext/

Gaffer tape it is

Any recommendations on a 20ish litre (or higher) compressor that's quieter than the cheapy options?

Does anyone know where I can hold of a bracket for rack stays that can be bolted through a seatstay bridge brake hole? Basically a steel strip, hole in the middle, 90deg bends each end, holes there. I have def seen something like this out there in the wild…

I’m regretting not adding rear rack eyes to a frame I had altered!

One of these? (Pictured)
https://www.lfgss.com/comments/15849227/

Can check if I have a spare later

I don't has, but these are bookmarked for whenever I want a kompressor
https://www.implotex.de/silent-compressor/1500w-2ps-18l-silent-fluesterkompressor-druckluftkompressor-60db-leise-oelfrei-fluester-kompressor-compressor-implotex_911_2701

Seat clamp with eyelets incorporated as an alternative?

Not on this bike, no.

Yes! If you do … please! I guess I could bodge something.