big time differences...a friend of mine just put in a JDM Vigor motor and harness into a USDM Vigor and it was a nightmare. He had to cannibalize parts off the broken USDM motor to make it work, including crank angle sensor (different plug pins), egr, water pump, driveshaft splines...uhhhh! it must've been a hell of a test of patience and not getting frustrated easily.
The JDM has different emissions than us and so their EVAP and O2 sensor stuff will be different. Their ECU's run off 100 RoN octane fuel trim.
I am oing through the same thing right now. It's not as bad as the Vigor. Actually everything is pretty straight EXCEPT that the Main Engine to chasis connections are flip flopped. The Pos Battery connection is easy enough to swap( Just use the USDM one) but I don't see a way around the main connections. I have heard that it has been done but I see no way to do it. I am tempted to bust open the Harnessflip it back. (LOL) My question is would there be a problem to just leave the extra connections un connected? I am sure it is fine if you are using a JDM ECU but if you are using a USDM Ecu I am sure it will through a code or two.