the problem is that if you buy a gc8 engine you may not have the correct propshaft, and will surely not have the correct driveshafts. the gd models are slightly longer and wider. then you also need to make sure you're also buying the brakes, knuckles, wiring..you also need a new meter panel as the 1.6ts meter has a 6200rpm redline so you need a gd wrx meter cluster. Then add the fact that the gc8 engine would be almost 20 years old.......hmmm
in short, if you opt for the gc8 engine you're screwed. your car will be a mess and you will not enjoy your ride even more.
how slow is your 1.6ts anyway? pm me for help
regards