if your 5gal corney keg fits upright, you should. Best case is it can fit 2 and a CO2 tank along with a bit of headspace for connections. Or maybe you can drill a hole and mount the CO2 on back. Either way, you'll need to drill a hole in the top for a tower. Just make sure you arent drilling into critical components of the fridge, although most of those should be right in plain sight at the back
I just took the plunge and bought a ready assembled 2 tap kegerator bundle deal with the kegs, CO2 tank, and all the connections. I'm not too handy so I wanted to save myself the trouble of building one myself. Plus, thats hours that could be spent brewing more beer...