Time's up.
OUAQUKGF Ops was correct with his pre-bedtime brainstorm - the 1961 Potez 840:
Only eight built - one fuselage on a farm in Shetland!
Triangular windows - did the Caravelle designer have a hand in this?
https://en.wikipedia.org/wiki/Potez_840
Reminiscent of a four-engined Jetstream:
I wonder if it would have been successful if suitable engines for a twin had been available? Four engines for an 18-seater must have made for expensive operating costs.
OUAQUKGF Ops has control.