> From: oldhippie
>
> And didn't "Wimoweh" become "The Lion Sleeps Tonight"?

And wasn't that a sordid tale of greed, and plagiaristic and racial exploitation?!
Rian Malan's story for Rolling Stone Magazine

> From: Richie
>
> Johnny and the Hurricanes recorded a rock and roll instrumental version In 1959 of the song entitled "Red River Rock" which became a hit in both the U.S. (#5) and in the UK (#3).

Are you referring to A:Rocking Goose / B:On Top Of Old Smokey - AIR, trad tunes played on a kazoo or similar?

> From: Genie
>
> A folk song that Ewan McColl wrote for Peggy Seeger to sing, "The First Time Ever ...

... I Saw Your Face" (to state its full title). According to legend, the remarkable thing about that song was that it was written during a transatlantic phone call between MacColl & Seeger. It's been covered not just by Roberta Flack but countless other pop stars, such as Celine Dione.

Also:

The Shadows - Quatermasster's Stores, originally Quartermaster's Stores.

East Of Eden - Jig-A-Jig

ELP - ISTR various versions of classical pieces, though I'm not sure any were actually hits.

Second City Sound - Tchaikovsky One - Theme from Tchaikovsky's First Piano Concerto popped-up in the 60s

Waldo de los Rios - Mozart40 - Mozart's 40th symphony popped-up in the 60s and since used as a sport TV theme.

John Denver - Annie's Song - Theme from Tchaikovsky's 5th Symphony

60s comic song 'Hello Mother, Hello Father' and Walt Disney's Fantasia (scene that begins with ostriches as ballet dancers) both used a well-known classical tune (Amilcare Ponchielli - La Gioconda - Dance Of The Hours).

Many more pop plagiarisms of classical here:
Pop meets the Classics

Surely someone, somewhere must have had a chart hit with John Henry?