Engine swap is easy bit!!! its the little thoings that you have to do that make the conversion that much harder to complete,
for instance, engine mounting are in a different place,
yes, but its stock!

easy to get.
there wont be the extra set of exhaust hangers for the twin system on the smaller one,clutch on the big engine is hydraulic small one cable, so the pedal box has to be done
i have hydraulic clutch on X20XEV... it shares fluid with brakes, maybe SOHC engine has cable?!! ,
the brakes wil need swapping for the big ones ,
nope! late 2.0 have same brakes with 3.0 cars, 296 mm, i dont know how much it mean in inches, but these are the biggest stock rotors for omega available.. plus after stock discs worn, i changed them for cross-drilled Zimmermans

Never tested the difference, but it makes me happier

the axle in the smaller car has the small flange on the drive shafts, so you will have to swap the rear axle for one with the big driveshafts, and to get the correct gearing for the big engine, the dashpanel will have to be changed , along with teh ecu, which means the key etc etc etc I could go on and on(whatever gives you the idea Ive been there before) 
yes its possible to do but its a lot of work and whatever time frame you set yourself add at least 6 weeks to it!
Omegatoy
Yep... i totally agree with the rest... The easiest way is to get a donor car with all necessary parts fitted, it can be bought for relatively cheap - about 3-4 KUSD... Maybe it can even be a Vauxhall

i've seen a lot of them breaking in poland
