The sceen was supposed to be taking place in 1970, which is when the song was a huge hit on the radio.
However, it did NOT sound like the original version to me. I've heard that Jim Peterik and the rest of the guys from the Ides re-recorded the song back in the late 90's or so, and I'm wondering if that's the version I'm hearing in the film?
Never thought I'd see the name JIM PETERIK listed in the end titles of a horror film!

