Fixing crack on 330g some advice

[Black Phantom]

I'm not sure that your overflow will have less pressure as the pressure at a given depth is independent of direction -- it is the same in all directions.
I have a large tank myself and just knowing how much time and effort went into the tank as far as livestock, corals, liverock etc, I would replace any glass that might have had it's integrity compromised. Everyone here has seen what a couple of spilled gallons can do let alone hundreds. Your investment will end up being in the thousands of dollars by the time your done. Don't cheap out just to save a couple of bucks