Most threads I've seen where the outcome has been both durable and brilliant have used Duplicolor or VHT brand paints. Both have formulas rated to 500* F, and each has a "cast aluminum" color available.
A common technique appears to be pre-heating the case before painting to purge as much grease and contaminates out of the cases, a final cleanse and rinse with Acetone, then primer/paint. Curing in the oven is also highly suggested.
I hope/trust those brands are available in Oz. I think Dave500 just referenced one of them in a recent reply as well.
