I'll have to get back to some of the 'Aussie boards to verify this, but I'm pretty sure the landcruiser R151 shares the same output as the US R150F 5spd that comes behind the v6.  In which case, you could just shop Marlin's site like you have a R150F.  To run dual gear driven cases, you'd need the V6 adapter plate, and the dual ultimate.   But... you might want to hear from Marlin before you go spending your money.  Pictures would help out with identifying everything.  How do you like the turbo diesel?

HF1A or HF2A ring any bells for anyone?  not sure if these are 'split style'...