[WKB]

Merv,
There are some big power nissans that are used in all types of motorsports using the R200 differential.
The R32 GTST rear end that is mainly used has a 4.3 to 1 ratio. The R32 GTR rear end has a 4.1 to 1 ratio. GTR rear ends can be used but as there are slight differences between the GTR and GTST rear ends and there is a fair bit more fiddling around to fit them(I speak from the experience of fitting a GTR rear end).
A couple of cobras I know that have 4.6 ltr quad cam fords and GTST rear ends that use second gear to take off most of the time. One has a T56 and the other one has a T45 gearboxes.
As Craig said the best way to find out what is right is to drive the car first, then modify if needed to suit your needs.

Warren