if using a socketed P28 which is OBD1, you will also need an EK1 > OBD1 harness, OBD1 dizzy & wire the injectors cuase Y4 has 2 injectors to 1 wire, whereas OBD1 has 1 wire each injector...

EDIT - if using a Y4 or non-vtec head, you dont really need the P28 ecu, just get a P06...