frob,
Thanks for the great tips on de-warping and filling the holes.
I need to find my IR digital thermometer (my shop is a mess!) so I can monitor the 100% duty cycle max heating and I'll try the recommended procedure to flatten the board before I try to level the heated build platform. The LAVA is off the Hadron again at this time, so it's a good time to do this. I'm well along my way in the steep learning curve that has me assembling and disassembling to add or change something on a regular basis, but I'm nearing a convergence of electromechanical solutions. At least I think I am.

There's not much more to add, so future disassembly and reassembly will be to correct problems discovered while debugging and testing. I guess that's progress.
I wondered if the very nice standoffs on the LAVA contributed to the warping, but I had decided to chalk it up to the PCB fabricator. I've gotten some curly boards before.
I was going to try printing on Kapton film as I had read some good results from that, but at least for now, I've decided to go with the more conventional glass surface, partly to help with the flatness. If I decide to try the Kapton film, I'll fill the holes as you recommended.
I appreciate your attention to details and the aesthetics of the LAVA. I'm being probably a bit too fussy about the Hadron appearance, but I'm also pushing for a tidy build to make it more robust. I'm treating the build more like a hobby, but I'm justifying the attention to details as an investment in reliability. If all goes according to plan, I'll be doing a lot of 3D printing.