Small steps.
The heater core was looped out of the system, but fortunately the heater hoses were left in place. We re-connected them and added about half a gallon of coolant to the system. The heat blows nice and hot. Also of note, the AC clutch turns on w/the little green button on the dash, so we know at least part of the AC is working.
I also got my cable in for the 14cux, and was able to get RoverGauge up and running. Handy to have the ability to interrogate the ECU, I may look to get it up and running on a tablet or raspberry pi for a more portable solution. You can see here that we're running R3038 - a generic Defender 3.9 tune. I need to sort through all the ECU's we've got around here again and see which ones are socketed, then I can get a tune that is more suited to the 4.6L - there's likely a fair bit of performance left on the table.
All in all - another good day, getting more and more comfortable with this engine at every turn.
Before I start searching - what's the best method to burp these things without getting coolant everywhere