(off topic): obscure Beefheart?

This afternoon I discovered an oddity among my old 45's: a promo copy of "Hard Working Man" w/Capt. Beefheart on vocals. It was apparently from the score of "Blue Collar" (1978) and the credits list Jack Nitzsche, Ry Cooder and Paul Schrader as the writers. Could anyone shed some light on this disc or what led to such a fortuitous grouping? jm