Having just come back from the
2006 Great Escape, I don't think you want either a rally car or a Datsun.
Any half-way decent rally car will be too noisy, too low geared, too uncomfortable and too hard to get bits for in the middle of nowhere. And you won't be pushing hard enough to make use of the good points of a rally car.
Having said that, some rally features are good things - most people use 4WD tyres and their cars handle like crap because of them... Similarly, decent 'rally-spec' shock absorbers would help heaps...
When Paulie and I decided to go on TGE, we were both thinking about rally cars, but we quickly realised that was not a good idea - the real priorities are reliablity, comfort, and ability to traverse moderately difficult terrain. And ability to find bits out west of Triple Buggery. Most people end up with old Holdens/Falcons/Chryslers, and they meet the criteria quite well.
We took a nearly standard Volvo 244, and it was excellent. It could have done with better shocks, and more attention to dust proofing, but we had zero problems with starting, fuel consumption, corrugations, overheating, brakes or handling (unlike most of the Australian cars).
It was consistantly difficult to drive as slowly as 98% of the other cars (remembering that speed isn't the object like it is in a rally).