In that case a transplant sounds like the go.
Being a holden you might get lucky with some commonality in the gearbox department. Try Marks adaptors at
http://www.marks4wd.com/ to get an idea of what they can supply in the way of kits. This will give you an idea of what others have done before you - no point in being the pioneer unless you have truly bottomless pockets.
This is a good site when it comes to weighing up your options - Michael thought it out thoroughly and weighed up all the pros and cons - a good model to work from.
http://www.cmr.uq.edu.au/~rotor/the_shed/Rangemobile/
I would think the Holdens are the way to go - lots of aussies [Hilux, Suzuki, etc.] are swapping out their 2.? diesils and small petrols and putting in VT6 commie engines which are plentiful powerful and cheap...