Buy a universal one from FCPGroton (new), I think about 45 dollars.

Not sure about the 87, but you could also go to your local Autozone and get the O2 sensor made for the Ford Mustang -- the wires are shorter, so you will need to splice them with your existing harness. Good thing is it cost only 38 dollars, it is the exact same sensor as the one for Volvos 240 and Autozone land you the tool to remove the sensor for free. Ford Mustang Bosh sensor is part N° 13913.

I would not put in a used O2 sensor, even if it still good, you don't know how much life it has left. At 30 some dollars go with a new one.

I have used the Bosch 13913 back in February and have been very happy with the results, here the thread for information

http://www.brickboard.com/RWD/index.htm?id=747077

For single wire, check out Dave Shannon's site (a lot of other useful information on his site) :

http://www.homestead.com/volvo2/O2sensor.html

Good luck.

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'89 244DL M47 161K miles