With caution in mind, I ordered a couple of cheap mics partially to avoid harming my good mics if I've got the phantom power wrong but also because I'll need another pair for outriggers in the 5-mic set-up.
Then a couple of hours later, overcome with impatience, I tried it with one of my good mics. No smoke. But no sound either. Power to the mic & opamp seem fine. With headphones on the monitoring side of my recorder, I can hear a little mains hum when I touch either of the output wires. But nothing when I touch any of the input wires. Maybe the 100k resistors are too high?
The way I've built the alpha prototype means I'll need to desolder the input/mix array from the opamp board in order to test if the opamp side is OK. I will also explore with an oscilloscope tomorrow. Meanwhile I'll add a pic of the alpha prototype in all it gory.