Don,
The difference in concern is with the cylinder heads used on those engines.
Each have their small differences, but they offer the same basic thing: a removeable intake for much improved breathing. The Aussie head and the US heads can interchange exhaust manifolds, so that's a plus. However, they are getting rather scarce to find, and in well used condition when they turn up. Argentine heads use different manifolds, but are currently being re-produced.
If you need more specifics on the Argy heads, send me a PM.