Benny & Joon audiences stuck on the burr-inflected theme song, ''I'm Gonna Be (500 Miles),'' have the movie's star to thank. ''I told Mary Stuart Masterson to bring in her favorite music, as motivation in the scene where she's painting,'' explains Jeremiah Chechik, who directed Masterson as a schizophrenic and Johnny Depp as her oddball suitor in the film. ''She brought tons, but when we started playing the Proclaimers, I just thought, Man, this is too perfect a romantic song about someone who will walk a thousand miles, or act crazy, or do anything for true love.''
''It's a very simple, straightforward rockin' love song. That's it,'' says Charlie Reid. He and his identical twin, Craig, constitute the Proclaimers perhaps the greatest neo-nerdy, quasi-evangelistic folk duo to come out of Scotland. Considering the recent success of songs from The Bodyguard, Aladdin, and Indecent Proposal, this may be the band's big break. ''When the song came out in America in 1989, we did okay on the college charts, but there was no action on the main chart,'' says Charlie, who is currently working on the pair's third album. ''Hopefully when that comes out people will remember us.'' For ears too eager to wait for the Benny & Joon soundtrack, due out later this month, the quirky tune is available on the Proclaimers' 1988 album, Sunshine on Leith (Chrysalis).