Ive got 2 drilled tanks and one with a hang on overflow. Drilling is really the way to go IF its feasible. I have had the tank runnning for 2 months with the hang on overflow. I did alot of research and bought a Life Reef overflow. Im very happy with it and knock on wood.. its been flawless so far. I turn my pump off at least 2 times a day to feed, and it has always restarted no problems. The guy that makes them says he has never had one fail to restart.
http://www.lifereef.com/frame.html