My Century put down 260rwhp bone stock, and that's through a power-sapping auto. I reckon they have well over 300hp out of the box, and you'd free up lots more power with a better flowing exhaust (stocker has 4 cats and 7 mufflers) and a manual transmission.
SEVEN Mufflers? Wow. Such silent, very restrict.
edit: MK Bruin, seven mufflers seems like a lot, this car must be very silent, what do you think?