This isn't a vouch, but I have been researching shops in the Southbay to help me out on my near future build of my 3GS. The 2 names that keep on coming up are Status Autoworks in Gardena and 168 Motoring in Torrance. Like I said, I have no first hand experience with these 2 shops, but I will probably contact them soon.
Let me know if you do contact them and your experience if possible. Cheers.