Hey Dan,
I am so excited you started a thread. I'm about a month behind you on a project that's almost exactly the same (just a little smaller). You're pictures are great, and I'm looking forward to drilling the holes for my calfo overflow tonight. Did you use 2x4's to hold the overflow in place while you levelled it and siliconed it in? Do you think it's necessary to put in a third (emergency) overflow drain?
And how are the returns from your dart set up? I was also planning on putting two holes in the bottom, and having the returns travel under the sand to the front, blowing towards the back of the tank. Then I would have the other two returns coming over the top. I'm currently debating on getting the OM-4 as well.
Either way, I'm excited you started a thread. This way I can just copy everything you do.
By the way, I liked your little hose setup for cooling your drill.