Speaking of non-Nissan conversions, a TVR engine would be nice, but could you imagine finding parts for it should anything go wrong (which eventually it would, being a TVR).. Shame too because TVRs are beautiful designs and hell fast.
I wonder if anyone has put a BMW M3 or early M5 (E34) engine in a Z. They are NA and make a shedload of power stock and parts would be more plentiful than a TVR.
I don't really like mixing and matching brands, but if I were to go for anything outside of a Nissan in my Z, it would be one of those.