RaspberryJAMMA + 4 player add-on board would plug directly into your NBA-Jam, including player 3 and 4. You could use your existing Pi3 with it if you wanted to, but you would likely have better results with a Pi4 or Pi5 for Midway games (Pi3 is good for CPS1/CPS2 using MAME0.172 though). Pi5...