2" exhaust is fine. If your positive you already have 2" then just get a highflow cat and the twin loop replica you were talking about. I know X-Force do a replica Mugen twin loop muffler so you might want to investigate that cos they are only a few hundred dollars.

obviously mandrel bent exhaust is better but if you've already got a 2" exhaust and it isnt mandrel bent i wouldnt waste my money to get a whole new exhaust just to get a mandrel bent exhaust.. you wont notice the difference especially on a NA car.