It's not REALLY easy mate.
Depends on your local rego laws as to what you can get away with. The Z24 engine transplant would be Illegal any many Aussie states.
I say you need to get used to the engine and car, and learn about it, before diving into an engine transplant.
You'll thank me when the car stops on a country road, no passing traffic, no phone reception.. You'll need to know how to troubleshoot it yourself.
I don't want to hear about you on the news.. "Young fella in Datsun starves to death by the side of the road"

From your sentence structure I'm guessing you are 17 or 18. Unless your father or uncle is a genius with a well stocked garage or a mechanic, you will have trouble performing the conversion, and trouble maintaining the car properly.
If you are older and have PLENTY of cash, you can either go buy a new V8 Mustang, or spend similar money fixing up your Datto. The choice is yours. At least with the Mustang you can buy it under finance. Very few banks will give you money to fix up your Datto.
Reality sux, but if you want anything bad enough, you will make it happen.