The ECU/harness will make the vehicle illegal for operation on US roads. The car is already illegal, so maybe this isn't of concern to you.
OK, that's not too bad then.it’s only 8 pins i’ve gotta repin in the harness and then the TGV from original motor has to be transferred to the jdm motor.
All good advice...what seems to have slipped through, moderator, is this "I’m just worried about the condition of the car after sitting for so long in his yard. This is the reason why i’m trying to get it back on the road for as cheap as possible so that I can confirm the car is even worth saving before I drop 4k on a built short block from IAG. " That aspect seemst o have been overun by engine advice.Then why is there any question? This isn't a half ass your way through life project. You can detonate an engine in minutes if you fudge your way through this.
There isn't all that much power difference. Not enough you would even notice.
I wouldn't chance 3-5k to save 5 bucks. Thats just bad math. Do it right the first time, or this isn't a project you want to take on. These "junkyard find/build/blahblah" youtube channels have placed an unrealistic image in peoples minds of how this kind of thing works. You don't just hodgepodge a bunch of bs together and have a reasonably functioning car.