Thank you, it's not my work but it's mine. . It requires to be embellished now.
To be honest, this adapter is for my chewlix, to play a ringedge 2 system with 6 buttons (and tx2 too). I am not mentally and financially ready for an exa system.
Since you're just using the IO for controls, you could pick up any IO board and skip the supergun entirely. You just have to make an adapter between your supergun controller and the digital inputs on the IO, and wire a small +5V / +12V PSU to power the thing.
What about a SEGA MEGAPLAY SYSTEM motherboard +
Streets of Rage 2
Golden Axe 2
Bio Hazard Battle
Sonic the Hedgehog
Sonic the Hedgehog 2
Shinobi III
Mazin Wars
(coversion cartridges)