I distributed Pennzoil on the South Coast/Southern Tablelands for many, many years until I sold it to the North Coast distributors at the time (DealQuip) Last I knew Harrigan Ford were the distributors in Wollongong.
Pennzoil has a huge range. Still, the best suited oil for the Red Holden V8 from their range is mineral Pennzoil GT Performance 20W50 SF/SH
At a push Straight Pennzoil HD 40W although not suitable for colder areas.

That said, all the major oil companies offer great oils. Just stay away from "Friction Modified" oil's like the old Castrol GTX.
Friction Modifiers are Plastics (like Teflon) and anyone who has ever lifted a valley and seen the dry cracked clay bed look or tried fishing the the plastic sludge in the sump will be aware of why I don't recommend friction modified Castrol oils.

Regards, Smooth