I understand that obd2 is different that obd1 I am an ASE master certified technician with over 15 years in the business 12 of which has been spent working on hondas, don't try to talk to me like I am a moron and listen to what I am saying.
The engine harness that is on the b16a2 (99-00 civic si) is a direct plug-in for 92-95 honda civics, there is no need to change anything on your car to accept the engine (except if you own a Vx which isn't the case here, For example if you have a complete donor 2000 si, all you do is unplug the engine 2 plugs on the driver's side right by the clutch master cylinder resivoir and either 3 or 4 plugs (off the top of my head) on the passenger side right on the shock tower , pull the axles and shift linkage, disconnect the exhaust manifold from the cat, and pull the whole thing out of the car, then you simply drop it into any 92-95 civic put the axles and shift linkage back in and it will run and drive. The great thing about doing a swap into a Cx is that you eliminate the cat since it is manifold mounted on the cx engine. No need to change mounts or anyhting.
Since you have a Cx it is equipped with only a 1 wire o2 sensor and does not have wiring for vtec or the knock sensor. In order to make it work 100% you will have to run wires from the ecu to various spots on the cannon plugs where the engine plugs in so it will work.
here is the artical for the 4 wire conversion:
https://hondaswap.com/swap-articles/1-wire-4-wire-o2-conversion-32519/
Here is a link for the vtec and knock:
https://hondaswap.com/swap-articles/obd1-b-series-wiring-guide-29111/
Finally, the p28 ecu is obd1 I looked just to make sure, you will not need to modify anything on the 93 civic in order to plug it right in.
If you have any other questions post back.
Also, just about anyone here on hondaswap can vouche that I know what I am talking about (unless I am really tired which happens from time to time) so please do not offend me with inane remarks.