Since you are 16, you should find out how much a sports car cost to insure. If you get past that then you can decide how much you can spend on engine swaps. Some options are L28/turbo (easy), Chevy V8, Ford V8, Nissan RB20-RB25, SR20, they all fit for $$$.

 

Tons of swaps. But at your age, unless you have a father that is a VERY good mechanic and is willing to build a car with you, I wouldn't recommend it. Z's are awesome cars, but remember, they're old and act like it. Doing a swap is going to be very involved. Lots of fabricating. You can swap almost anyhting you can think of, it will just be a lot of work. you can do 7mgte, 1jz, 2jz, VG, RBs, sbc, any v8, there's tons of options, look on hybridz.org for more options.