all the engines you listed will bolt into a MK2, plus a few more as well.
The fuel tank is the same on carb and injection models, just need to fit the in-tank and under car pumps plus matching fuel lines. 8v GTI manifold is the same bolt pattern as the carby, but the GTI one is a better design. You could fit the carby one to a GTI head but I'd go with a GTI setup. If you wanted to stick with a 1.8 8v GTI all you need is the head, the bottom end is the same as a 1.8 carby one. Still need the rest of the injection gubbins of course. 2.0 8v either fit the rest of the 2.0 8v injection stuff, or fit a 1.8 8v GTI head to the bottom end and fit MK2 digi GTI stuff.
16v requires a different zuast manifold, you could fit an 8v GTI downpipe to the manifold and fit it to your old zaust, but from the factory the 16v had a bigger bore on it so I'd go with a proper 16v one. 2.0 and 1.8 16v require the same ammount of work to fit, so go for a 2.0 if you can afford the insurance!
