I looked up the ferry company and asked via email:
Saw your company flight planned a C172 from St. Johns/CYYT to Billund, Denmark/EKBI the other day. Surely there have to be intermediate stops along the way… What route does one use to get across the pond, and does your company do anything to extend the range of a C172?
To which they replied:
The aircraft had a 124 US gallon fuel tankinstalled in Bangor, ME to give it more than 17 hours of range. We frequently fly them nonstop from St. Johns, Newfoundland [CYYT] to EINN, or possibly Jersey, or possibly Billund, Denmark, or Egelsbach, Germany if we have good winds.
A truly impressive (and anonymous) feat of flying, it reminds me of the early transatlantic pilots back in the 1930s (but with GPS).
I am going to look up in my POH what 124 gallons does to the gross weight of a C172!