I installed and adjusted the gantry last night without the Y axis pipes. (I didn't have enough parts 'in stock' and I couldn't seem to wait until I had another trip to the hardware store.) Pics to follow.
I've built the X axis and gantry from scrap 5/4 decking, so I've had to adjust the dimensions slightly. I seems to be working fine, it's dimensionally stable, and the best part is it's free (left over from a nephew's decking project). I'll be using scavenged steppers (I have 4), so instead of the belt I'm going to try dual motors on the X axis. Also, I've built my own stepper drivers based on PMinMO electronics designs that I've made 'modular'.