You need a high pressure fuel pump, fuel pressure regulator, injectors, sensors, throttle body, ect... oh and something to control all those things :D
A lot of the simpler aftermarket programmable EFI units just use your coil to get RPM signal, some you have to set up with a hall effect sensor on the crank, some need to be setup off the cam. I believe the older nissan/datsun EFI systems just get RPM signal from the dizzy.
It basically comes down to your buget and what you are after with the car. If you can get by with using an older OEM system, and figure it out, then go for it. If you want something you can tweak and play with, check out any of the aftermarket EFI computers.