Another option is getting an external overflow box . . . I had the same dilemma when I started out. In my case I decided that it would be best for me if I don't get the tank drilled . . . CPR makes the BEST overflow box IMO/IME . .
might cost you abit tho (anywhere around $100-$200 depending on size / brand) . . . for ur tank
The brand that Im using is a cpr-cs50 paid for $120 and does about 300GPH
My external overflow pic . . . (beside the powerhead on the right side of tank)... depending on your rock/coral structure you can hide the box if you want to . . . in my case . . . I could care less if I see it or not. . . as long as it works
another shot . . . angled view
Cheers-