I have done some crazy stuff over the years, but I wouldn't have modified the plastic frame without secondary reinforcement. I guess it really is never too late, but I would really suggest adding a glass center brace between the front and back just in case. Granted, I have done some crazy things with glass boxes, but keep an eye out for stress fractures in the plastic above where the part was removed.
Either way I love it. Glad to see others drilling glass like its no big deal. I do like the stealth style overflow boxes a lot.