[smokinreefer]

do you mean you want to silicone in an overflow box in the center and have the drain holes added to the bottom for your herbie?

yeah, thats a good plan. but then i would just plug the current holes up and do an over the top dual returns.

or you mean just drill holes and have standpipes as your herbie?
and then run standpipes up from the current holes as your returns?

short answer, No. I wouldnt do it that way.
i prefer to have as little holes on bottom due to paranoia of leaks.
if the hole is on bottom and it leaks, potentially whole tank drains.