It's Mound Dawg.....another renegade from the AROC forum!!.
Jools, I use Millers Classic Sport, semi synthetic in mine. It seems good stuff.
We had a tour around the Millers factory with the owners club a year or so back. the tech guy was quite adamant their 20w50 Classic Oil (A mineral oil) was perfect for the Alfa Nord units, he only recomended Classic Sport for hard track type use. Mind you I still bought classic sport, even though I didn't intend to track the car.....then!.
So to answer your question Yes Millers Classic is fine, and brewed in Yorkshire too
The semi synth in mine drips out very slowly through some of the seals, but I don't think it's a problem and it doesn't seem to burn much either. Some of the modern fully synthetics would probably leak through the seals much quicker.
Not sure about HPX though, whats that?.