As best as I understand the case, there are two main suspects :
1/ Arthur Stanley BROWN - although Brown lived in Brisbane, he travelled a lot and was believed to be in Melbourne in 1973 and perhaps Adelaide in 1973 as well. His own relatives claim he molested children and only ill health saw him avoid going down for the 1970 murders of the Mackay sisters. As per the post above, he had an absolutely striking resemblance to the identikit sketch from the Adelaide abductions, even down to the wide brimmed hat.
2/ Stanley Arthur HART - Hart was a notorious sex offender who also looked uncannily like the identikit sketch, including the big ears. Hart, unlike Brown, also lived nearby. Much of the information linking Hart to the case seems to rely on the memory of his incarcerated, convicted, pedophile grandson Mark Marshall, who was only 3 years of age at the time of the Adelaide girl's disappearance. Marshall presented about an 80 page submission to the inquest and to me it reads like the work of a twisted guy in jail with too much time on his side. However, it is Hart who is linked to the barrels that blood samples are being sent overseas to be tested from.