No! Not only are they physically different sizes (the probe that goes into the exhaust) but the connectors are different. Not only that but the "rear o2s" aren't even that. They are what Ford calls a "catalyst monitor". They both measure the amount of oxygen, but the HO2S1s operate on a broad range from about 100mv to 900mv and switch constantly having many cross counts. The Catalyst Monitor or HO2S2 operate between 300-400 MV and do NOT switch much. Even if you were able to splice the wires and "make it work" and it functioned correctly, the longivity of the sensor would be reduced. There is a reason why Ford spent the time engineering 2 different sensors. Seriously just get the right sensor...
Mike
