The 02 sensor will be screwed somewhere into the exhaust system. It will look somewhat like a deep socket screwed perpindicular to the exhaust pipe. Mine was down under the car right in front of the Catlyitic convertor facing inside. Some are up under the exhaust manifold. 240's have a thick green wire on the firewall, passenger side, that runs next to all of the other wires routed there and then it connects to a black rubber boot that conncects to a smaller black wire that will run to the 02 sensor. So try and find the green wire, I can't imagine they changed the setup from 240 to 740, it would look like around an 8-10 gauge wire size, or trace down the exhaust system from the manifold until you find it and then trace the wires back. Yours should have three wires coming off of it. The wire that connects to the green wire is the one with the signal that you can test. After the car has run for at least three minutes the sensore should be generating, I don't have my manual in front of me, around 0.4 volts to a little over 1 volt, and should constantly fluctuate also change the throttle when reading to see greater fluctuations.
My analog meter can't read the signal so I just went ahead and put in the inexpensive model to see if it worked and it did. The other two wires on these sensors are just to preheat the 02 sensor and in my opinion are not very important. You will need a special socket to remove the o2 sensor as the socket will need to fit over the wires.
Hope this helps, let me know if you have any other questions about it.
Does your car have the onboard diagnostic computer? The one where you just press the button and it blips any trouble codes to you?
Do you have any manuals for the car?