A muffler shop should carry most suplies to make an exhaust.
I am using the Flowmaster 80 series#42583.
Not all shops carry all makes and models of mufflers though.
2.5 inch pipe from the converter back to the muffler is a good size with a good sound.
That flowmaster has 1 inlet and dual 2.5" outs, so you can hav duals out the back
Other companies do make mufflers that are simular.
Should be several pipe shops around where you live.
On plugs, I stick with AC Delco's Iridiums, they last along time, and dont faul out easy.
Several options on the wires, most people just stick with GMs wires , any high quality 8mm wire is good though.
btw- headers run around $600. I paid $750 years ago, a real pain in the a**(pita) to put on
