During Hollywood’s Golden Age, being a star entailed more than just acting: leading men and women had to sing, dance, play it straight, play the clown — in short, they had to know how to entertain.

Little wonder, then, that in 1958, when the Academy of Motion Picture Arts and Sciences planned its 30th Oscars ceremony — the fifth ever to be televised — it called upon the town’s multi-talented silver-screen icons to do what they did best, and put on barn-burner of a show.

LIFE photographer Leonard McCombe was a fly on the wall that year as stars from Paul Newman and Zsa Zsa Gabor to Kirk Douglas and Mae West dropped in to rehearse for the big event. As it turned out, however, only a handful of McCombe’s marvelous photos were ever published. Until now.

In this gallery of rare and unpublished pictures — the kind of candid, revealing shots that are nearly impossible to capture today, with so much about Hollywood’s big night shrouded in secrecy — screen legends put their egos on hold, roll up their sleeves, and go to work. The result? Sheer showbiz magic.