Hey,
you can get a 180CA18DET for cheap around australia ,
RB26DETT you can get one out of a 33GTR with the box etc etc.
im not to sure about the 25tgearbox you will need more information on that.
you will need to get the car engineerd for dropping the a rb26dett inside .
also you will need r33 gtr brakes and some goot suspension and good rubber. the car will loose lots of traction dont forget. maybe itll requite 255's or some wider rear gaurds.
its alli can think of.