It's true, there is a difference with California legal and Federal legal emission requirements. And, for the most part California is stricter. However, a USED vehicle (such as your 1999 Subaru Legacy) which has all the Federal required emission components, can pass the California smog inspection process and be legally registered in this state.
Now if you want to make sure your Subaru Legacy's emissions will pass California emission cutscores, we recommend obtaining an emissions test in your State before moving to California and checking those scores with California's Emission Limits. The emissions which will be tested are HC, CO, and NO.
The website you want to access in order to find out your Subaru Legacy Outback's current California emission cut scores is below:
California Emission Cut Scores