just saw this thread. I am the one who put a rb26 in the z32 and am in mobile, al. As far as the COG - the engine sits farther forward about 6.5" and sits a little lower overall in the car. the car actually weighs less with the rb26. As far as price, i got my motor for a steal. This swap may not be for everyone, but it is nice to be able to change the spark plugs in 15 minutes and to not worry about how many days it will take to change out the turbos. I am not knocking the vg engine, but i am a tall person and it was hard to work on that thing.
I know a lot of people will argue about the performance of both engines and they are great, but my preference is the rb and its capability to pull very strong in the high rpm range.