Hollywood, 1971: the year of Dirty Harry and The French Connection, Klute and The Last Picture Show, Vanishing Point and Two-Lane Blacktop.

It was one of the most inventive periods American cinema has ever known, and out of its midst came one of the most unique cult films of all time: Harold And Maude, directed by Hal Ashby, the tale of an emotionally neglected rich kid who falls in love with a free-spirited 79-year-old woman.

Considered a box-office flop at the time, Harold And Maude's reputation and cultural significance has grown to the extent that, in 1997, it was selected for preservation in the National Film Registry of the Library of Congress. Viewed today, it's still laugh-out-loud funny (when Harold is trying to shock his mother into paying him attention by staging ever-more elaborate fake suicides) and thematically daring (when the two lead characters' relationship becomes, well, more than platonic).

In 1980, screenwriter Colin Higgins reworked his material into a stage play, and it's a pared-back version of this that will premiere later this month at the Tron. Director Kenny Miller has trimmed away the excess of characters that Higgins crammed into the theatre version, thereby sharpening the focus on the central pairing (played here by Tommy Bastow and Vari Sylvester, who have the somewhat unenviable task of stepping into the shoes of the film's stars, Bud Cort and Ruth Gordon).

"Casting is always difficult when you do a stage version of a film that everyone has loved," notes Miller. "Especially this film, which is iconic because of these two performances, these two actors. But with the stage play, you connect to them instantly. You're watching real people portraying these characters, and you link to them the way you do your gran or your mum, or an odd brother or an odd uncle – because they're standing right in front of you."

Miller doesn't see the story as scandalous, although he admits that, while there are plenty of instances of old men marrying young women, it's rare these days to hear of a scenario with genders reversed. "I suppose, in modern times, a lot of people look at a relationship like that and think of it as being really quite unsavory," he says. "But it's only late on the sex comes into it, and that's because Harold finds Maude such a beautiful person. It's the beauty that he finds sexually attractive, the beauty of a person, not how old she is. She has opened his eyes to a new life and, before she passes away, he has given her another sense of freedom."

The play falls under the banners of both the Glasgay! and Luminate festivals, not that Miller is directing it with any festival brief on board. "I just think it's a fantastic story," he insists. "I'm simply doing it because two people fall in love. Although they happen to be extreme age ranges, they do still fall in love."

Harold And Maude is at The Tron, Glasgow, October 30-November 3, www.glasgay.co.uk, www.luminatescotland.org