The only problems with a swap into an Hx is the 5 wire wideband O2 sensor, and the fact the Hx doesn't have a Fuel Tank pressure sensor.

You can buy a 99-00 Ex or Si harness to get around the primary O2 sensor wiring...but then you will have to add wires for the secondary O2. It probably would be easier just to modify your existing harness.

Without the fuel tank pressure sensor you will be throwing a code 91 after you take the car out a few times.

The ECUs I found that didn't throw a code 91 was a 96 gsr.

You don't need to worry about the EGR becuase pretty much any engine you swap in won't need one.