One hell of a lot, apart from the obvious (engine, trans) you would need computer, diff, suspension. Basically take the guts from a VZ for example, and fit it to a VN shell.
Some guy in NZ did it, full conversion, cost around 10-11g all up. Just buy a VY wreck and do the transplant. Not easy, but anything's possible with the right amount of time, money and patience
nope, dont bother, Sell what ever you have now and trade up to a VT II SS or soemthing with an LS1, you can pick up up for around 11-12k anyday of the week..
Cheers