"The fact that the two us should be chosen to be part of this as an homage -- an overall collective homage to the piece -- is just delicious," said Pearl. "That has been the 'Grease' experience all the way along. It's been one magical moment after the next."
In this new version of the rock 'n' roll paean to puberty set in the 1950s, Conn, 64, will play a waitress at the Frosty Palace malt shop, while Pearl, 65, plays a TV producer.
The pair will join stars Julianne Hough as Sandy, Aaron Tveit as Danny Zuko, Vanessa Hudgens as Rizzo, Carly Rae Jepsen as Frenchy, KeKe Palmer as Marty and Mario Lopez as Vince Fontaine.
Conn said her first meeting with Jepsen was emotional. "I started to cry. I think partly it was 'That could be my daughter that I never had,'" said the actress. "She is absolutely yummy-adorable."
Other cameos will be done by "Saturday Night Live" alum Ana Gasteyer, "Brady Bunch" star Eve Plumb, "The Fresh Beat Band" star Yvette Gonzalez-Nacer and "The Wire" star Wendell Pierce. A live audience will add a dash of theater, which won't rattle Pearl or Conn, both stage veterans.
The 1978 hit movie starred John Travolta and Olivia Newton-John. Over the years, Pearl and Conn have become the keepers of the "Grease" flame, organizing reunions and protecting the actors' copyright. "He's the troop leader of the T-Birds and I'm the den mother," said Conn.
This time, they added their deep knowledge of all things "Grease." During rehearsals, Conn noticed the boys in leather jackets weren't being nearly amorous enough around the girls, while Pearl pointed out that the script called for the guys to high-five but no one did that during the Eisenhower administration.
Pearl, whose link to "Grease" started when he joined the first national tour in 1973, said natural changes have crept in over the years. For instance, on Sunday there will be no f-bombs or cigarette smoking, and the lyrics for "Greased Lightnin' have been sanitized.
But the broadcast will have a lot of Broadway DNA. It's being directed by Thomas Kail ("Hamilton"), with music supervision by Tom Kitt ("Next to Normal"), production design by David Korins ("Hamilton") and costume design by William Ivey Long ("Cabaret").
After the film version of Grease, Conn went on to do "Lost in Yonkers" on Broadway and voiced the animated film "Raggedy Ann & Andy: A Musical Adventure."
She said there's a reason "Grease" never dies. "'Grease' is about firsts -- first love, first car, first heartbreak. For Frenchie, first career disappointment," she said. "It's a story of excitement and newness and energy."
For Pearl, who made his Broadway debut in "Bye Bye Birdie" and also was in "Oliver!" it's all about finding a surrogate family of friends: "At the core of it is a group of kids that just love each other."