I had an O2 clamp on my automatic P5-T, it worked well until I installed a 626 manifold and then I started to hit fuel cut every time. You'll also need a rising rate fuel pressure regulator to go along with it, I used a BEGi back then.. it was kind of the standard combo for the few of us that had turbomatics back in the day.
If you want to know more about it, I remember writing up a How-To on TMF (The Mazda Forum) for both the BEGi and the O2 clamp. Feel free to look it up if you truly do decide to go down that road. If you encounter problems or have any major questions, I'll gladly help but keep in mind that it's been over 5 years since I had that setup so I'm not very likely to remember much..