Heart and Soul came out in 1938; featured in "A Song is Born". You'll note in the biography to the right of Larry Clinton, the Glen Gray/Casa Loma Orchestra is not mentioned, but it is in the article I referred you to in the previous post on Sentimental Journey.
This bio does mention Ferde Grofe, whom I know to be the composer of the Grand Canyon Suite, not as a swing orchestra leader. Apparently he was that in a previous incarnation.
Anyone who has ever played piano (and some who haven't) is familiar with the tune to Heart and Soul. It rivals "Chopsticks" as a piano duet or solo!