as far as the love of the game goes, there really are unlimited options for a motor for your z.
personally, i love the idea of a 6 cyl turbo diesel cummins in a 240 as a drag machine (wouldn't much be able to see over the hood, but the sucker'll fit)
however, as far as practicality goes (hah), I only see two options for my car: l28et, or ls1.
l28et (the turbo l28 motor) is just so damned easy to swap in, and once it's there, for $15 you can get a manual boost controller, and just dial-a-horse.
the ls1 is more complicated, and once it's in, it's in, and there aren't a whole hell of a lot easy ways to get more power (this is true between any naturally aspirated motor vs any forced induction motor).
Maybe the romantic in me just loves the idea of a cheap power gain. "sorry, girl, all i can afford is this brass piece of valve."
and she loves it so much, she gives me a 200 horsepower gain.
LOVE IT!