It is possible but costly in money and time. Here's what we know...
- Keyboard schematic is available. https://www.atariarc...e_Atari_400.php
- PCB is 109 x 287mm and the position and dimensions of mounting notches and holes can be copied from the existing keyboard assemblies.
- We need 61-63 keyswitches laid out in a matrix. Ribbon cable header with 0.1" spacing. Spacebar stabilizer mech is still unknown, but just pick a good one and use it.
- I purchased two SP DSA keycaps and confirmed that the unmodified keycaps should work with a low profile switch. Key height will be 1/8" taller than B-Key keycaps. http://atariage.com/...oard-atari-400/
- To have SP manufacture the keycap set, they need AI or Inkscape drawings of the 4 custom Atari arrow keys. Can be 4 separate files or all in one file. Manufacturing time is 10 weeks from payment, but shipped to one person who will need to split and reship to individual buyers.
- The Cherry MX low profile switch seems to be only available to keyboard manufacturers at this time but will hopefully be more widely available later in 2019. Initial reviews seem to indicate that these are smoother than the Kailh low-profile switches for off-center keypresses, but it protrudes from the bottom of the PCB, so the metal supports on the shield may need to be cut down.
- If blank keycaps are used, will need to sketch and dye sub or laser etch the custom Atari keys.
Personally, I prefer the dark PBT doubleshot keys and MX low-pro switches as I think it looks closest to an 800, but that is $900 for one prototype and out of my budget. I have no experience with Kailh switches but they seem to have a loyal following. I think the Kailh keycaps look more like XE style, though. If you don't mind lighter colored keys, then the Kailh setup will be more economical and easier to fit.
I also contacted MaxKeyboard about a set of R3-only keycaps. Their process produces one set of R1-R5 keycaps according to their template, so a set of R3-only would require 5-6 passes at extra cost. They offer limited keycap colors.
I don't plan to pursue this project further. If someone wants to use this information and continue on, feel free to do so. I can also let my contact at SP know if you want to pursue the PBT doubleshot keys. If you need help with sketches or 3D-printed brackets, I'm willing to help too.