The two-door hatchback was essentially one of just 33 produced by Holden and is considered one of Australia's most sort-after muscle cars.

"This is the holy grail of Holden motor collector cars," Lloyds Auctions chief Lee Hames said.

"Since Holden closed their doors many muscle car enthusiasts have been mourning the loss of performance cars."

Holden built the 33 A9X hatchback shells in 1977, enough to last the expected racing life for the model.

They were double seam welded, all painted white and sold exclusively to race teams.

But Lloyds said there was considerable uproar from rival teams when the word got out the shells were built with thinner gauge steel, making them considerably lighter than standard production cars they were supposed to mirror.

Internal and external pressings, such as hinges and bumpers, were also lighter and even the glass in the rear hatch was one-millimetre thinner.

Holden said the variation was a result of changing to metric measurements and after an investigation threatened to withdraw from racing if the shells were not approved.

Three of the shells were bought by racing team boss Ron Hodgson, who immediately had two built out for the track, keeping a third as a spare.

Two years later, after the model was to be replaced with the first of the Commodores, Hodgson gave instructions to build the untouched shell into a road car, which is the one up for grabs on Saturday.

The car has just 475 kilometres on the clock.

Mr Hames said with recent high prices paid for rare Holdens, he wouldn't be surprised to see a record for the Torana with bids topping $1 million.

In recent auctions, one of the last Holden Commodores to be built in Adelaide sold for $750,000, another A9X Torana sold for $910,000 and a Holden Maloo Ute sold for $1.1 million.

Australian Associated Press