I don't have any shop info for your 87 but I THINK this is how it is setup:
Look for the Thick Film Ignition Module either right on the distributor or possibly over on the inner fender. 4 wires run from the TFI Module to the ECA (aka PCM). I believe that your ECA is under the passenger side kick panel but I don't know that for sure. The connector that is removed to set the base timing is called the "SPOUT", it is inline in one of the 4 wires and probably looks vaguely like an inline fuse holder. The SPOUT may be somewhere along a yellow/green wire - at least that's the color code for a 1989 Ranger. When the SPOUT is disconnected, the ECA no longer controls advance and the base timing can be set. AFAIK
, the timing should be 10* BTDC but double check on the underhood label or in a shop manual to be sure.