I think a lot of pilots don't realize that the Goose Bay-Greenland-Iceland route does not involve long distances.
A little history on this route. In the early stages of WWII there were very few operational cargo aircraft larger than a DC3. The northern route was developed based on the limitations of the DC3. Goose Bay, Greenland and Iceland airports were all built or greatly expanded in the early war years.
The Greenland airports were all named Bluie West with a following number. This was a result of US Navy surveys with each area being assigned a letter of the alphabet. On this route the designation was apparently only used in Greenland.
The longest leg on this route is roughly 800 statute miles. The Piper Twin Commanche can fly this leg eastbound with only the optional factory tip tanks for additional fuel. Total fuel 120 gallons, 114 useable. The TC can fly the longest leg on 1/2 of that fuel. On the Greenland leg this leaves adequate reserve fuel to reach a distant alternate.
The problem on this route is weather, it is likely to be rotten even in mid summer.
In the post WWII era I believe the first to do this in a light airplane was Max Conrad in a 125 hp PA20 Pacer. Two round trips Minneapolis to Switzerland. This led to a long career ferrying small airplanes all over the world.
In the early 50's Peter Gluckmann flew a 90 hp Luscombe from San Francisco
to Berlin, round trip. He had some limited instrument training but was not instrument rated.
Much later Mira Slovak did it westbound in a Fournier motor glider. It has been done in an ultralight.