coast to coast

[Dive_dry]

So I am building a new tank and want to do a coast to coast. I would like to do an external overflow but have bin told it would weaken the glass. The tank is 330 g 72" long x36" front to back 30" tall glass is 3/4" or 19 mm . So my question is will it weaken the glass as i would like no obstructions in the tank nice and clean as it will be seen from 2 sides hopefully still designing the basement