Steve, The Link G4 GTiR/ S14,S15 plugin literally plugs right in. The only thing I had to change was the speed source as the input to the ECU came from the back of the speedo and the link didn't like it. Just had to tee off the wire that came from the vehicle speed sensor into the speedo, a 10 minute job. Also you have to run a tube through the firewall for the MAP sensor and a wire for the IAT sensor but there are ways of using the factory MAF wiring if you aren't planning on going back. Only thing you may need on top is aftermarket knock monitoring for tuning but if you're taking it to a dyno then no worries. The G4 has a very impressive list of features. I am a complete noob and have managed to get it all installed and running myself including sorting out idle issues and started the fuel tuning.
I also installed a wideband at the same time and that was more of a hassle than installing the link.
I also installed a wideband at the same time and that was more of a hassle than installing the link.