This will work for USDM OBD-1 ECU’s:
Read the code on it. The 2nd to last # on an automatic ECU will have a 5.
If it is anything but a five then it is a manual ECU.
For JDM OBD-1 ECU’s:
Reade the code on it. If the last 3 digits are 900 or 901 it is an automatic ECU.
Information Source: www.hondaswap.com