Whew, with several engineering problems solved with a rotary tool, diamond bits, and a lot of thinking, here's the light mount. Also used were a hand saw, miter box, and an electric drill.
From almost direct front, imagine a tank up to the joint in the back.
From a little above.
Here it's fully extended upwards, as it would be for maintenance.
Here's a picture of how it's mounted to the stand, removable with four screws. I had to add some balsa shims at the bottom to make up for the top extending outward from the frame. It's plenty strong...
...but it's really hard to tighten the wing nut with just fingers to keep the light from slowly drooping down. Once I get the stand in place, I'll put the tank in place, and then install the block so that won't happen.
The back of the light fixture.
If anyone has any questions on how I did anything, feel free to ask.
Finally to putting polyurethane on all the wood after some sanding. I'm not putting any time frames on anything anymore, I'm always behind schedule on this project. Oh yeah, the balsa shade...