Yes, but there are inevitably differences in what the engine harness connects to on the body side. You need to work through both harnesses and sort out the differences. So, actually, the answer is no, if you just want to drop it in.
You will need to generate a 0-5v square wave speed signal to give to the ECU and other computers so they don't freak out. The ECU less so, seeing as you're using Haltech, but the ABS computer (and auto TCU if present) will want it. The stock speedo head does this for you, and if you remove it.....
The differences you will need to sort out pertain to alternator wiring, air-con wiring (if you're going to use R34 parts), gearbox loom wiring possibly, plus the probably differences in the ECCS relays and other relays near the ECU.