The SR20DET is a lot more powerful than the one that we got in america. The KA24E we got was also used in nissan trucks in america. It's got more displacement and is made for low RPM torque, not rev happy HP. The SR20 is a bolt-in if you wanna swap it. It's a very common swap. There are a few mods available for the US engine, but there are like coutless ones for the SR20. Here's how sportcompactcar magazine did their swap.
http://www.sportcompactcarweb.com/tech/0205scc_silvia/
Have fun if you end up getting that project car. Wish there was a cheap 240sx around here...