Pasquale Lanciana was jailed for 14 years in September 2021, after a County Court jury found him guilty of organising or participating in the June 1994 robbery, falsely imprisoning the guards and laundering the cash.
Posing as workmen, an elaborate roadworks site was set up by five thieves wearing goggles and helmets. They started up a concrete saw to distract an Armaguard van driver when they pulled up at the fake site.
The group then handcuffed three security guards at gunpoint and placed plastic bags over their heads, before driving off through the backstreets of Richmond. The stolen money has never been recovered.
Lanciana, a former kickboxer, was convicted of armed robbery, false imprisonment and seven counts of money laundering and must serve 10 years before he is eligible for parole.
He has launched an appeal of both his conviction and sentence, claiming jurors were improperly directed before retiring to deliberate their verdict.
His barrister Tim Game SC told the Court of Appeal on Tuesday the prosecution's directions to the jury at Laciana's trial may have led individual jurors to arrive at their guilty verdict for different reasons.
"You could have any number of jurors, say seven, find him guilty of being present but not organising, and any number of jurors (find him) not present but organised," he told the court in Melbourne.
"By virtue of these directions, you've now got different acts...with different bases of liability."
Mr Game said if some jurors found him not guilty of planning the heist then he should be acquitted.
Prosecutor Diana Piekusis KC said there was evidence at trial that Lanciana had organised the robbery and "this is not a circumstance where one theory may exculpate the alternative theory".
Lanciana, who appeared via video link from prison, is the only person ever charged over the heist.
He was arrested in 2016 and spent more than two years in custody before receiving bail when the jury at his first trial in 2019 could not reach a verdict.
Justices David Beach, Stephen McLeish and Maree Kennedy adjourned the court to consider their decision.