I sent you a PM about the card...so no worries
You can double wire it, you will have to use some connectors for the wires between the test switch, volume controls, coin doors, lights, etc...it will also take a little time to put it all back to a GDL since you have to swap the roms and hard drive, swap the main harness, swap the extra control harnesses, swap the control panel harness and then rotate the joystick boards 90 degrees. I had both GL and GDL that I could switch between, but decided to just sell the roms and hard drives since I re-wired the harness and went to a dedicated Sportstation.