I installed the cap on the degassing tank first, crossover plug was last. Sorry for the confusion
Degassing tank/resevior was full so I did not add any coolant in there. The 2 gallons 50/50 Motorcraft Gold/Distilled water all went in via the crossover tube.
Car will definitely be making its way in to see a "qualified" mechanic though, just to be safe.
Thanks for the replies.