O. R. U. [Off Road Unlimited] in Burbank is an excellent choice (a little outside of your requested area). They do a lot of custom builds and regular installs of aftermarket components. 818-563-1208 or 818-848-2020.
They do a lot of straight axle conversions, and custom builds for magazines.
Staff is very experienced. I'd feel more comfortable with them than a place like 4-wheel parts which seems to do mostly wheels, tires and lift kits.