The 1.4 Gearbox doesnt always fit the 2L engines, iirc its more like a polo box, or at least its not a 020 box, im sure it will fit but clutch/fly wheel might be diffrent.
You will need:
GTI engine
Gearbox (maybe)
Exhaust system (including cat)
Radiator + Fan assembly
ECU and Engine loom
Dash loom -Optional depending on what you are adding (e.g elec windows) usually easier to use the GTI loom
Fuel pump? cant remember what pressure the 1.4 is but iirc you DONT need to change it
Of course when you think about the other things that you should change, it makes sence to use a doner car, like rear suspenssion beam, rear brakes, front suspension, front brakes, anti roll bar (if you dont already have one) etc.. If you have a doner car you can just pysically change everything that is diffrent, that method worked for me

Oh and as for the gearbox, i would use a GTI box, the 1.4 boxes are weak, the GTI box struggles to cope as it is so i dread to think what the 1.4 would be like
