In the meantime, I did find this version of the song by the Blue Diamonds. History doesn't tell us if they were considered for the Dutch national final in 1968, but they did record this single, which didn't make the Dutch top 40. It still is a good version, and the B-side is a charming piece of music as well. The Blue Diamonds were best known in the Netherlands for their single 'Ramona', a huge hit that caused many Dutch parents to call their daughters Ramona as well.
My collection: 7" single no. 6725
Found: Discogs.com, received 9 June 2022
Cost: €4
Tracks: 'Someday (Morgen)' / 'Angelina (Liesje)'