NavList:

Antoine Couëtte you asked: “would you be so kind as to indicate "your" London and NY coordinates used in your exercise ?”

The lat & longs I used (or was given; I can’t remember) were:
London: 51° 30’N 000° 05’W
New York: 40° 43’N 073° 59’W
WGS 84 Earth radius at the Equator 6378137m
WGS 8$ Earth radius at the Poles      6356752m

You also asked for my end results.  All this was clear in the photographs, even on my Motorola G7 ‘Power’ smartphone.  However, pour mon ami:

Spherical Trig

Initial Course to London from New York:  051° 13’ 07.32”
Initial Course to New York from London:  228° 21’ 10.8”
Great Circle Arc: 5,577.886km
Longitude for course = 270/090: 023° 03.3’W

Ellipsoidal Trig

Geodesic London to New York: 5,586.662km assuming you stand on the same spot on deck when you arrive that you were standing on when you set off.

Initial Course to London from New York:  051° 14’ 50.3”
Initial Course to New York from London:  228° 23’ 32”

Quoting values to one metre and 1/100^th second of arc are of course purely academic, but I was happy to go along with it, because I’d been forced to buy my first scientific calculator (Cassio fx-992s about £12GBP – still sitting in front of me) and was keen to try it out. 

Antoine
I must stress that I submitted this calculation 25 years ago when I still had a few grey cells left.  Sadly, these days, I’m down to my last two or three, so I'm unlikely to be able to explain any more than I have done already.  DaveP