I was very pleased with Awesome Performance in Rancho Santa Margarita, 949-858-9898. Two years ago they did a complete custom job on my 62 - re-routed so both pipes and cats were inside the framerails. It's much cleaner than the original design. The total cost with 2 new cats, 1 muffler (Magnaflow, IIRC) , exhaust and tail pipes was $650. I shopped the job around and their price was best by far. They've also done work on my carpool buddy's 40's, and he's been pleased with both the prices and the workmanship.
It's a hike from the South Bay, but they do Saturday by appointment only. Many years ago there was great muffler shop in Inglewood, at the corner of Market & La Brea. I don't know if they're still in business, same owner, or anything else, but if you're in that area you might swing by and check it out.
Good luck,
JR