Bubblyrat - Indeed, "No other love have I" was adapted from "Beneath the southern cross" from Richard Rodgers TV score "Victoria by the sea".
"Stranger in Paradise" is a theme from the "Polovtian Dances" by Alexander Borodin.
Other examples (classical composers): "The world outside" (by "The Four Aces)is based on Richard Addinsell's "Warsaw Concerto". "Till the end of time" by Jerry Vale was taken from Chopin's Heroic Polonaise.

And here are a lot of other (non-classical) vocal remakes of instrumentals :

Because you're young - James Darren

Moonlight Serenade - Vaughn Monroe

Raunchy - Webb Pierce

Charmaine - The Bachelors

Take Five - Sarah Vaughn

In the Mood - Andrew Sisters

Washington Square - Ames Brothers

Apache - Sonny James

The Harry Lime Theme - Donald Peers

To be honest, I must confess that most of this wasn't what I did remember. Many thanks to the internet.

Manfred