Take a look at this thread that discussed the lamda tower and adjustment:
I'm watching with interest because both of my cars barely passed the last smog test. Both were at the max limit for Hydrocarbons. The basic remedy is "replace the cat and the O2 sensor and you should be fine". Wow! That will sure add up!
I'm hoping that there is somebody out there who has installed a universal O2 sensor and can report back with their experience.