Together they wrote another novel and several TV miniseries.
Then one night Ossana read Proulx's story, "Brokeback Mountain" in the New Yorker.
"I knew immediately it was a powerful story that could touch many people and I wanted to get it out in the world in some major way," Ossana recalls. "I thought we should write a screenplay. So I raced downstairs, I found Larry, I said, 'Would you read this story' and he said, 'You know I don't read short fiction.'"
McMurtry's explanation: "I can't write it. I've never written a short story."
"Right, so I said, 'But will you humor me and read the thing, okay,'" Ossana adds.
The result: "I thought it was the best story I'd ever read that addressed the American West. I thought, why didn't I write it myself. And I thought that it is a great story and it will go around the world," McMurtry says.
The pair quickly wrote Proulx to option the work for film.
"We felt that we had a very, very rare opportunity. You just don't get material like that in a normal life as a screenwriter, just once in your lifetime, maybe," McMurtry says.
The subject of homosexuality, pervasive throughout the story and film, may, on the surface, run counter to the tastes of McMurtry's fan base, though the author says he was never concerned.
Ossana says, "I just flat out asked him, I said, 'Is it going to bother you or affect you at all if some of your, ya know, fans think that this is you standing the West on its head or something.' He said, 'I've never given it a thought and I won't.'"
"It never occurred to me," McMurtry adds.
They wrote the screenplay as they always do: McMurtry working on one of his nine Hermes typewriters and just bangs away.
"You know, I have no ideas until I sit down at this machine. I can't talk abstractly about anything. I have -- don't think about it. I do it at the same time every day and whatever process I have starts when I hit the keys and stops when I get to the end of five pages," McMurtry says.
Ossana adds, "I take his five pages and I might reduce them to two three or I might expand those to eight or 10."
They finished "Brokeback Mountain" in three months, but it took seven years to get the movie made.
McMurtry and Ossana don't believe producers or directors were scared away from the film's subject, rather, actors' agents. As McMurtry put it, actors had to deal with whispers around Hollywood that a role in a gay cowboy film was "career suicide."
But everything changed when noted director Ang Lee came aboard. He already knew about McMurtry.
But it was the story and the screenplay that sold him.
"I cried and there's something twist my gut," Lee says. "And you read this screenplay, you don't doubt at 30 pages can turn into a movie. You see a movie right in front of you."
Jake Gyllenhaal and Heath Ledger signed on too, untroubled by playing gay characters.
"Not being gay, I knew that would be a challenge for me and knew that that I could use that as an advantage," Ledger says.
But everyone connected with this film insists is that it is much more than an iconoclastic depiction of love between two cowboys.
"It doesn't present any kind of agenda, any politics at all, one way or the other at all," McMurtry says. "It just says life is not for sissies."
He elaborates, saying, "Ya know, you need strength. Love is not easy. If you find it, it's not easy. If you don't find it, it's not easy. It's not easy if you find it, but it doesn't work out, it merely says, the strong survive, but not everybody is the strong and many people don't."
"Brokeback Mountain" has garnered more Oscar nominations than any other film this year – eight in all -- including best adapted screenplay for Ossana and McMurtry. They've already won the same award at the Golden Globes.
But winning the Oscar for "Brokeback Mountain" is definitely the pair's goal.
"If you compete, you wanna win," McMurtry says laughing.
Ossana adds, "But it's a, ya know, again, it would be just an affirmation for everyone who's not just everyone who's worked on the film, but in my mind sort of everyone who as seen the film, too."
McMurtry and Ossana believed in "Brokeback Mountain" despite their own manager's first reaction.
"I said, 'It's a story about, it's a doomed love between young ranch hands in 1963 Wyoming,'" Ossana recalls. "And he said, 'Are you outta your mind? Just forget about it Diana. It'll never get made.'"