well if ur ever in the area I can tell ya where to go, otherwise I'm not really familiar with Huntington Beach area.
Make sure the muffler shop has all the necessary equipment such as mandrel bender, quality welder, wide selection of mufflers and tips (even though I wouldn't suggest buying them there at marked up prices), etc. Oh yeah, ask a welder how long he's been doing it for.
Since you're in Socal, try to negotiate prices. I'm sure you can find a good place to weld everything for like 100 bucks.