Today's progress was small but important: I soldered wires onto the hotend heater and the replacement Thermistor, and then glued it in with some JB Weld that FabLab fortunately is in possession of. I do believe that was the last piece that needed mounting, and the last wires that need soldering (except perhaps the cooling fan, but that's an optional part, so it doesn't count).
Next time: figure out why the Z-axis gets stuck (needs oil? Bad rod?) and test the extruder!