I've received two different answers to this since Graeme posted.
4WD INDUSTRIES - 4x4 Parts & Accessories stated they did not think standard 18" alloys would fit on the V8, however the poster of the gumtree ad stated they would fit no worries, but I don't really trust him!
The uncertainty around this makes me a bit nervous, would obviously prefer 18" but am also considering the Maxis AT980 on the 19s.

