C2C weir cut

[gregzz4]

Look online. I remember seeing a site that showed how far from the edges to drill. It discusses glass thickness and hole sizes. Remember that you want your overflow box to be 3 or 4 inches deeper than the top of the weir.

[gregzz4]

One other thing. Do some research about the weir height. With a C2C the water flowing over will be very thin so you won't need to cut very low. I'm thinking 1/2" will give you lots of wiggle room as I'd be surprised if the flow is even 1/4" thick.
Figure out your potential flow rate and look around the web.