So yesterday afternoon, my kids helped me cut the glass for the overflow. I was quite pleased with the results. First, we semi cleaned up the glass to be cut (it was full of silicone and fish water residue). I got this 3/8" glass for trade for some other clean 1/4" glass that I had sitting around in the garage, so I'm not complaining. Here are pictures.
This one shows my 2 outside walls of the overflow and the divider. The kid's books was just used to prop the glass up will breaking it along the score line.
This picture is to show that I got pretty close to 90 degree cut. I was surprised that the newly cut edges were not sharp. I could run my hand up and down the fresh edge quite comfortably. Sorry for the fuzzy picture (cell phone camera)
And here my son being a goofball. He was helping me with the breaking of the glass. This picture shows the fresh cut
Hopefully today or tomorrow I can drill the drain holes and assemble the box. I have to get a wire brush or something to clean the excess silicone of the edges though. I'm not too much of a fan of this. At least we have a bit of progress.