Just to clarify.. the ECM (Electronic Control Module) is not the same as the ICM (Ignition Control Module)..
The ICM is under the distributor cap.
The ECM (or computer) is under the right side of the dash.
If you are talking about the ESCM (Electronic Spark Control Module)..
It's on the right side of the blower motor housing,left side looking from the front....(at least in my 87)