rich or lean
 

i was told a long time ago that you can test for lean or rich conditions with a multimeter and you just hook it up to the o2 sensors but what should it read and is this even possible.

this is true, but you have to know how to read an O2 sensors "real time". it should toggle from .5v above and below rapidly. highest should be about 1.0v meaning rich side. .01 is lean. your 87 doesnt have a data stream. Fords used Breakout boxes. meaning you cant get sensor data unless you backprobe the circuit or use and expensive breakout box. your year only throws out codes.