I've build Atari 800XL and Atari 65XE USB keyboards before. I've also built a 65XE with an integrated Raspberry Pi. This one is a step further.
contact me, or see my Etsy store. I have the later version of this, the Atari 65XE USB keyboard listed, more info on that build in the blog post about the Atari 65XE USB keyboard and joystick with Raspberry pi 3.