Tom, you'd be better off getting the complete engine and then disposing of anything you don't need as whatever the seller offers you for the various bits you don't need will almost certainly be a lot less than what they're worth.
Also see my reply about the injectors in your other post, a lot of things might give you a "light bulb moment"!
With the exhaust, to be honest you're best off talking to the exhaust builder about how you want it to sound.
A good builder can make it do what you want and need it to do. A 2.5" exhaust should be about right for the 2.5L AQ151 though.
That said, because it has a much longer run from the engine to the tail pipes, a 2" system might well be much better as it will help restore low down torque and isn't any different to the standard size. It's all about pulse tuning and the volume of each pulse - not how loud it is but how much space it takes.
https://www.enginelabs.com/engine-te...gn-and-theory/
Have a read of that and do some of your own searches on exhaust pulse tuning, you'll soon get the idea! You'll also see why i'm suggesting sticking to the standard bore with the larger engine might actually be a good idea because of the length of it.
