Re: coupe engines
There are many posts on this. The 20v/20v Turbo engine will go into the HGT only - because it is a bigger engine than the 16v. The 16v/16v Turbo should go into the other models. Yes a rear-ended coupe would be best so you get a good engine.
As for the other bits apart from the engine. You will need the gearbox to take the extra power (+ it's 6 speed!!) and the brakes are a good idea. Your probably better off getting an after market exhaust to increase the power over a standard one.
A couple of people have transplanted the 20v turbo engine (220bhp) into the HGT, but I think there is only 1 person with a 16v turbo (195bhp) swap.