I believe all long tube headers are illegal in California. To make a legal set, you would have to make a matching set of headers and h-pipe, then get the whole system an EO#. The problem is that it is illegal to replace your h-pipe untill you are past 100,000 miles.
So, in 1994, or earlier, you would have to design an exhaust system that people will have to drive 100,000 miles to legally install. By the time that most '94-95 cars can install it, Ford is no longer making 5.0's, which means that the aftermarket will not support a market that is not growing.
Luckily, California only requires smog tests once every two years, so just use illegal headers and save your old parts to swap back at smog time.