Returning from Vietnam was a life-changing event for Mr Allen, who suffered the breakdown of his marriage and loss of contact with his children.
He had red paint thrown on him when he marched in his former home town of Adelaide and did not work up the courage to march again until 2002.
Although they make light of their friendship, it has helped them deal with the demons of their past and use their life experiences to help others.
As well as suffering from stress and anger management issues, he said he had health problems from Agent Orange, which was used by the US military during the war as part of its herbicidal warfare program.
They both encouraged other Vietnam veterans to join the RSL and not suffer in silence.