Replace the Guitar Hero PS2 Controller PCB with a drop-in USB HID adapter PCB. Uses Arduino Pro Micro as a generic USB HID device.
Extra details on my youtube video: https://youtu.be/DkvGg6Z6r1o
Pinout follows Daemon Byte Arcade encoder.
I did not get the whammy connected as it has an unusual range in the stock PS2 design.
Tested to fit this GH guitar model (for PS2)