Ok here we go. The gti are injection engines rather than carbed. your choices are the 8v or 16v gti. You will need then an engine, gearbox, loom, all hoses and pipes, airbox, fusebox.
I would say the best way of you doing this to find an entire donor car. As you have, you should buy mk2s of body condition so you should be able to buy a dirty cheap tatty gti and have everything you need.
While you are at it you should also take the rear axle and disk brakes, The suspension, the front brakes, the master cylinder, the servo. Basically put all of the gti into the driver.