In my other post, picture one. There is the oval thing just before the big round thing at the end.
That is where you bolt the exhaust to the exhaust manifold.
Your stock exhaust may be one piece, but it is not one piece with the exhaust manifold and cutting is not required.
The flange is to your left in this picture.
They only chopped the rear pipe from the exhaust because it would have been that much longer.
I repeat for the last time, no cutting is required unless you plan on keeping the stock exhaust.
Here is a better pic of the stock exhaust uncut.
And here is a pic of the flange that bolts onto to the stock exhaust manifold.
As for pipe diameter, don't worry too much about it. You are not racing the car so don't worry about every last HP. And you, with the larger diameter piping, you will lose some torque as there is less back pressure.
The Corksport is 2.4 inch ID, which should be plenty fine and not too big that you'll lose too much torque.