Drilling for herbies

[ReefJunkie]

I want to drill two more holes in my 65 but I need some advice. The overflow is 8" x 6" with one hole and I want to make it dual herbie style. In my search I found the general rule of drilling at least a hole width apart. Think I can get away with another hole in my overflow area? Here's a pic

I am also drilling a return at the top left.