I'm not saying an F20C would be slow either, and of course the F20C has more RWHP you don't see an L series rev to 8 Grand often.
I've honestly looked at this swap alot myself, But its already been said that the motor's are expensive, and need to have a lot of things adapted to the datsun, Throttle, Speedo Etc Etc.
You would probally end up spending much more than just the cost of the engine getting everything working, with the Z's electronics and other things.
But its not my money do what you please with it