I know this is a dumb question but what communication is there between the engine, its sensors, the ecu and the rest of the car?

The reason I ask is I am trying to do a 92-95 JDM H22A swap into a 00' ek and have discovered that the P13 ecu that comes with the swap is a 4-plug type.
I was planning on using a ex/si civic wiring harness and modifying it to fit the H22 but the civic harness is a 3-plug type.

What should I do? I would like to just be able to run the whole H22 harness that comes with my swap and run the P13 ecu (both 4-plug type parts) but I am worried that the obd1 H22 harness and ecu won't work with my 00' obd2b civic.

Can someone help me figure out how to put a 92-95 JDM H22A into my 2000 Civic Ex?!