Putting the group's 53-year career in perspective, their bond pre-dates the late American astronaut Neil Armstrong walking on the moon in 1969.

Lord mayor Robert Doyle describes the band as "genuine Melbourne legends", and a retrospective of their place in music history will be delivered in the musical Georgy Girl by a cast that has big shoes and instrument cases to fill.

For the cast announcement, the Seekers went back to the Sidney Myer Music Bowl, the venue of their history-making concert in 1967 when 200,000 fans packed in to see Australia's "Fab Four".

It isn't easy getting all four band members in the same place at the same time, but seated in the front row were Judith Durham, Athol Guy and Keith Potger. Absentee Bruce Woodley sent a video message.

The Seekers may have famously sang, I'll Never Find Another You, but the producers have found another talented four. Performer Pippa Grandison will play the pivotal role of Durham, Glaston Toft plays Guy, Phillip Lowe plays Potger and Mike McLeish plays Woodley.

The world premiere will have its red-carpet moment on December 22 at Her Majesty's Theatre. For a change, Durham, 72, will be in the audience and not on stage. With her trademark hair and sweet smile, she told Fairfax Media that she was honoured and proud that the musical was a Melbourne story.

When asked how she felt about seeing herself on stage, she said: "I will be in awe of it. It's a story of such significance to people, so obviously I won't know until the night how it's going to feel. At this point in time, I see there is a place in history for it and the music makes people feel good."

Grandison knows expectations are high for her portrayal of Durham, the Victorian of the Year, and will do it her way. "If I let myself feel the pressure, I think I would freak out," she told Fairfax Media.

"After speaking with the creative team and soul-searching, what we're after is the spirit of Judith. I'm not interested in doing an imitation or mimicking because I think that would be insulting. You will never find another Judith Durham."

The carnival never seems to be over for the Seekers. The group that first performed their harmonious folk songs in the Treble Clef cafe in Toorak Road, South Yarra, in 1962 have stayed together longer than many people's marriages.

Guy, reflecting on the group's five decades of unbreakable music and friendship, said: "It doesn't get better than this." While the 50th anniversary tour warmed their hearts as much as the cockles of those in the audience, he said the musical enabled him to reflect on his career in a deeper way.

"This, now, in its depth of understanding of actually what we achieved with those beautiful songs and that music in the '60s ... I refer to it as the musical Olympics of the '60s."

It's a tough ask choosing your favourite Seekers song but if you had to, it was Georgy Girl that made the group an international sensation. They were the first Australian group to reach No.1 in the US and it was nominated for an Academy Award for Best Original Song in 1967 after featuring in the 1966 film of the same name starring Lynn Redgrave as Georgy.

The musical will also feature the guaranteed sway-inducing and toe-tapping numbers Morningtown Ride, I'll Never Find Another You, The Carnival is Over, A World of Our Own plus others.

The musical's writer, Patrick Edgeworth, has personal knowledge of the group that was inducted into The Age Music Victoria Hall of Fame because he is Durham's brother-in-law. Four years ago, he thought the much-loved group could be brilliantly translated into a stage musical and approached producer Richard East, an original producer of the global smash hit Mamma Mia! There is added industry nous from fellow producer Dennis Smith from Dusty - The Original Pop Diva.

Previews of Georgy Girl begin on December 15 at Her Majesty's Theatre.