Getting it fitted like a scirocco 16v will take lots of time & money, since the required parts are very hard to come by. its not just the intake its also the airbox & fuel lines that need sourcing, all the pipework etc. you can bodge it using MK1 bits but that would defeat the point tbh.
The only mk1 sensors you can use from the old block are the coolant temp & oil pressure, non of the others will have any use on a 16v.
the enghine itself will drop right in usign the mounts swapped over from the old engine, and the old gearbox + flywheel. fit a new sachs mk2 gti clutch kit tho. If you want to use the 16v gearbox check the size of your driveshafts, if 90mm you need to swap your old box flanges over or fit 100mm shafts from a later cabby/scirocco.
what management are you planning to use on it? if kr all you need is a single pin black collar temp sensor for the ign controller, these can be found on many VAG cars, MK2 16v, MK1s, MK3 ABF etc. Same sensor as you need to use for the dash temp gauge basically. GSF sell em but I'm unsure of the quality of them. If you're going for the 9a managemnt, you need to get a lambdfa fitting in the downpipe, and buy a new ecu temp sensor from VAG. You'll also have a bit of wire splicing to do.
if you are going with the MK2/9a managment you need a MK1 GTI fuel pump, accumulator and lines. You wil lalso either need to swap the fuel tank for a MK1 GTI item, or drop in a later cabby/scirocco injection in-tank pump plus under car reservoir. Crazyquiff does 16v conversion pipes off the shelf, but a little pricy. Oh and you'll want MK1 metering head feed/return pipes plus the fuel filter bracket that fits to the front of the metering head.
If you want to run the MK2 16v isv controller ideally you want an early MK2 16v airbox as that will have all the correct connections on it for the over-run valve and the breather, if not you can use a MK1 airbox but fit the 16v metering head onto it. The late 16v airbox is too wide to fit on the driver side chassis leg.
you'll probably find you dont have much clearance for the dizzy, what you can do is fit an ABF dizzy cap and rotate the 9a dizzy 180 degrees, moving the leads round to suit. you'll need to use the 8v king lead though, or make your own as the 16v item isnt long enough.
Last of all the exhaust. You need to either buy an off-the shelf conversion manifold, or fabricate your own downpipe. the MK1 item wont bolt to the 16v manifold. You need to use the top half of the 16v downpipe welded to the bottom of the MK1 downpie, and some jiggery in between, like this:
With a bit of carefull thought and some effort you can fit the 16v so it looks liek it was there from the factory:
