Man! rb25det + that greddy manifold + one more grand and you get the Rb26dett... Better motor in every single way...
I did my math after getting a Rb25det, which I sold, and I'm just going to do the GT-R Stock Engine. Enough power, strong enough, and it is just a legend.
My recomendation: save money and be patient, get everything you need before start the swap.