Okay, I'm not sure what happened, but suddenly Genesis games work. I'm not sure if it was bad roms like @mitu said or if it was bad naming conventions on my end (changed both at the same time), but seems to function now either way.

Thanks again everyone for the help!

@mitu This is the exact slider i bought https://www.ebay.com/itm/1K-Ohm-Slide-Potentiometer-Pot-18mm-Pack-of-2/382238703800?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

It needs to be small to fit in the case!

@lostless aha, ok then.