Matt,
One minor problem is that Ford build their sixes arse about, ie with the exhaust on the driver's side. Nissan put it on the passenger side.
Silly question, by why dont you just turbo the Ford six? A 4.0 litre turbo will destroy any RB25, not to mention your trannie & diff. There are bucket loads of bits for turbo Fords nowadays, thanks to the XR6 turbo.
Also, try talking to Sean out at Adrenaline if your are from Bunno.