The forum has posts from 2017, so not sure if any are left. the kickstarter last updated last year, I do like that a modern keyboard. have you heard of Nanoatx PSUs they might work. Wow, wonder why these fail look at the $$$, if I could get a .cad file, I bet protocase will do it for much less. =https://www.kickstarter.com/pro2.5jects/505470364/the-x500-pro-computer-caseCooling would be an issue. You could cheat and hide the power supply in a 1541 Disk drive if it was tall enough?
Found this
https://www.kickstarter.com/projects/505470364/the-x500-pro-computer-case
or this
C64x Mini-ITX barebones with keyboard, etc.
https://www.lemon64.com/forum/viewtopic.php?t=62949&start=0