Wow, that's the same scene I recall seeing as a boy. Did you ever find the film? I'd love to locate it, too and appreciate any further insights. Thanks.
I remember something like this as well, from the seventies, they played it over & over many a Saturday afternoon. I remember it seemed to be a loch or lake in Scotland? Ireland? They had some kind of hideout, like a tent off of the road surrounding the body of water. I remember a girl & a boy.