I hope you don't mind me posting this here. As you know I have an Atari 800XL which has a Simius RGB mod and an Electrotrains Ultimate cart.
However some of my fondest memories were from the ST, so I created an Atari ST case for the Raspberry Pi. I've recently got a new filament colour that I think is pretty close to the original case.
I make these to order and usually ship in 7-10 days. I hope you like them.
You can run an Atari emulator using Retropie and the Hatari emulator as per this link: