Cheapest and best way you are going to do this mate is to buy a complete donar car. That way you will pay probably 10 times less and get literaly everything you need staright off
Unfortunatly you have a 1.2 so there for you are gonna need to uprate the brakes and suspension to take the extra 60-70bhp you'll be gaining.
Basic list needed is as follows.
Engine.
Engine Loom/Wires
All water pipes.
All ancilery pipes such as breathers and idle control pipes
ECU that belongs to the 2.0.
Custom made engine mounts (can be bought from Courtenay Sport as a pack)
If anything like my friend you may even have to change all the ignition barrel over to match the key that come with the donar car as most newer mototrs tend to have a chip in the ecu and the key, so when you start the car, the ECU can tell if it's the right chip.
Dont bother getting hold of a C20XE engine (Red Top 2.0) as you will be almost definatly have to pay out to get it reconditioned as 99.9% of these engine ares now driven into the ground. Instead just get the X20XE engine (Eco-Tec 2.0) remapped and jobs a goodn'.
There is nothing wrong what so ever with the later 2.0 engines, it's more down to rumours that this engine is no good. It's just cheaper and easier to maintain an engine that can still be bought brand new.
The best donar car you are going to find to be fair is most likly going to be a 2.0 Vectra or even a 2.0 Astra sport (you might be able to use the drive shafts from this car aswell but they are a little more than a Vectra)
#Also in getting the ectra you will also have a very good gear box to drop into your Corsa with the engine. If you get hold of a 2.0 Vectra SRi you will get the nice F18 gearbox or if you are lucky, the stronger F23. Both are 5 speed and both are quite strong. I left my F23 in my Vectra when I dropped a Red Top turbo into it and handled the extra power all day long.
Thing i've covered most bits there. Any further questions, just fire away
Cheers BAD63R