Thanks both of you for the info.

I will have to confirm but I believe the stock down pipe has been
replaced with a 4" unit by the previous owner.
The exhaust is a 4" aftermarket job.

The photo of the air filter looks very much like mine.
How does that seal with a snorkel?

Is there an Aussie supplier of replacement filters for the oilguard
or do they have to be sourced from the US as well?