By 1978 Leyland was importing the engines from the UK, so the rocker cover wouldn't have had a map of Australia on it. It would have been plain, without the big oil seperator bulge, with just a curved pipe coming out approximately facing toward where the radiator overflow is mounted.
The emission systems have usually been removed, I've only ever seen one fully intact one. The head will usually have some kind of blanking plugs across the front near the sparkplugs which shows where the air injection was.
An Australian one shouldn't be too hard to find, every engine had one.
cheers
Tim