2.5" is the correct size. Offset doesn't matter that much b/c you have so much room to work with once you remove the giant OEM muffler. The muffler you linked to should work, using the offset inlet/outlet.
Assuming you're having an exhaust shop bend up all the pipe for you, they'll make it work. Another option is to have the muffler sit at the back of the system, in the same place as the rear resonator, and have the tip tacked right to it. There are several 2nd gens that have this style done w/ dual exhaust. Pretty sharp.