(EW.com) -- There's no replacing Bill Murray, Dan Aykroyd, and Harold Ramis as the original "Ghostbusters," but if you were staging a one-night-only live version of the classic comedy, well ... whom might one contact?
Seth Rogen, Jack Black, and Rainn Wilson are going to cross the streams.
The event is one of the monthly live-reads of a famous movie script organized by "Juno" and "Up in the Air" filmmaker Jason Reitman, who — of course — has a family connection to this story. His father, Ivan Reitman, directed "Ghostbusters" and he remembers hanging around on the set as a little kid.
But even he was surprised when he went back and looked at the original script of the movie for Thursday night's reading at the Los Angeles County Museum of Art.
It turns out, Murray was making it all up as he went along.
"While almost all of the dialogue in original screenplay is echoed on screen, the Venkman character is completely improvised. It's as if Bill Murray was given a mumblecore-style essay about each scene and then permitted to say whatever he wanted as long as he got the point across," Reitman tells EW.
"He slimed me" is in the script, but not the follow-up line: "I feel so funky."
And remember Venkman's magician act?
It's not in the script.
"He's like a jazz musician who knows, 'I have eight measures here and have to hit this note here and as long as I follow those rules everything else is up to me,'" Reitman says.
Did that drive his father crazy? Reitman laughs and says: "This was his third movie with Bill. They'd made Meatballs, and done Stripes together. He was already familiar with those improvisation skills."
In creating the script for the Film Independent live-read this week, Reitman's father got him the original script, as well as a transcription of the finished movie. He found himself adding many of the improvisations to the page, while still trying to preserve some of the original lines, which have never been heard before.
"Every important Venkman line is back in there, and there are about 30 of those," Reitman says. "You can't have Ghostbusters without 'We came, we saw, we kicked its ass.'"
It's not just the memorable one-liners that Murray added. "It's the strange nuances," Reitman notes. "For example, Venkman goes to meet [Sigourney Weaver's] Dana at Lincoln Center and she's talking to a man. As he walks away, Venkman goes, 'I'm sorry you and I didn't get more of a chance to chat!' He expresses vulnerability and ego in a way that is kind of impossible to write."
That leads us to Reitman's choices on the live event's casting:
Seth Rogen as Peter Venkman
"It's the most crucial and tricky piece of casting. I knew we needed an actor whose rhythms were equally unique to Bill Murray's and had that kind of a swagger."
Jack Black as Ray Stantz
"When you think about Dan Aykroyd as Ray Stantz, you think about this positive enthusiasm and energy. No one has that like Jack Black."
Rainn Wilson as Egon Spengler
"As originated by Harold Ramis, this part needs someone with an earnest, scientific mind and clear-cut decisive humor."
The role of Winston Zeddmore, originated by Ernie Hudson, will be played by comedian and voice actor Phil LaMarr, best known for the role of Marvin in "Pulp Fiction." (Yeah, poor, shot-in-the-face Marvin.)
Weaver's role of Dana Barrett, a.k.a. The Gatekeeper will be played by Kristen Bell, while Kevin Pollak will play both the mayor of New York City and the fussy EPA idiot Walter "This man has no d—k" Peck. "Larry King and Casey Kasem both lent their voices to the original film, and Kevin does great impressions of both of them," Reitman adds.
Mae Whitman of Parenthood will take over the role of the "Ghostbusters'" receptionist Janine Melnitz, originated by Annie Potts, while Paul Rust (Inglourious Basterds, I Love You Beth Cooper) will perform the Rick Moranis part of Louis "The Keymaster" Tully. Paul Scheer will fill out the rest of the cast with such roles as the guy taking the psychic test at the beginning of the film -- and being mercilessly electrocuted by Venkman.
Reitman has previously staged Film Independent LACMA live-reads of "The Apartment," "The Princess Bride," "The Big Lebowski" and "The Breakfast Club," but this is the first time he has done one of his father's films.
"It was a part of my life growing up. I just thought it would be fun," the younger Reitman says. "I have one of the original Ghostbuster guns in my house. That is the one thing they want to see, and want to take a photo with. I understand the energy around that film. To me it's similar to The Princess Bride live-read we did last year. People have a relationship with the film that goes beyond normal movies."
The live-reads always sell out long before the film is even announced, but there is usually a wait-list outside and some people get lucky. For information about attending the event, check out LACMA's website.
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