the headers come with a downpipe.

You buy them, cut off the stock flex pipe and weld a ZZP 3in flex on them and then install on the car, the regular flex is not doubled walled and blows out within the first 10 miles for alot of people.

Porting the heads wont net much, but you can do it if you please, I would just get some rockers if you want a little more breathing room, but headers alone free up the exhaust a ton. Then port the blower.