And that conversion is popular enough that you want to check on that before you order. If you bought your bike used, the P.O. could have changed to a 520.
And, 14/42 is a large change from stock. I went 14/41 and was very happy with it on my GT, but I live in the mountains and wouldn't have gone as far if I did a lot of freeway travel. If I were you, especially living in SoCal, I'd try 14/39 or (preferably) 15/42 first. You might be satisfied with that much change.