Jim came by and we checked and double-checked the carb settings - no joy. The engine simply didn't start.
The fuel pressure regulator was set and it's currently just over 2.5psi. It may/may not need additional adjustment but it's not that big of a hassle. First hurdle is to get it running again.
After going through every possible scenario, we decided to pull the plugs and see what's going on - all four are black and wet. We quickly surmised that there is no spark - and then I remembered that I'd just swapped the coil. Bosch blue coils are notoriously mediocre in quality control and this one is likely bad. I haven't tested it out of the car but it (and the fuel pressure regulator) are the only things that have changed and the coil being bad would explain why this engine went from running like shit to not running at all. Another coil will be swapped in, plugs replaced and I'll try again. The one 'up' side is that I can install the thermocouple for the CHT and then I'll get to see how well that works.