[sllib]

I don't know if you have the skills to do this, but here goes: take your headers and side-pipes off of the car, check everything over for slag and funky welds and clean them up, then find a local company that does ceramic coating (your local Cobra club can advise you) and drive, don't ship, them there. I only say this because I've heard too many horror stories of pipes that were damaged in shipping. If your pipes are flanged this is a good time to clean up the interface between headers and side-pipes.
Most good shops can offer you a choice of colors to match your car. While the pipes are being done this is a good time to poke around under the hood for what's causing your back-firing which, I suspect, is caused by vacuum leaks so I would look for loose bolts on the heads and intake, and then leaky gaskets. There is a huge amount of info on the Web to help you. Good luck.
Bill