This is another of those 'can you do an XYZ USB keyboard', to which the answer is usually yes. In this case it is the Atari 400. I have a couple of Atari 400s I'm currently restoring, so I borrowed the keyboard from one of those for the purposes of testing the new board before I sent it off.
800XL and 65XE (which I have already done), just missing the 'help' function key on the side. The pins were in a different order again, so that's now at least four different pinouts for these 8-bit Atari keyboards, the 400, 65/130XE, and at least two different one for the 600/800XL.
If you want to order a kit to convert an Atari 400, you can buy one below. The kit include the USB keyboard controller, mounting pillars and a USB cable. You just need to supply the Atari 400.
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