your right i didn't know what motor is in your eclipse, it could be the 4cyl or the V6, since you said it's the 4G64 it would be the 4 cyl. The evo motor is a 4G63 which is a different motor then yours, it has different injectors, it's a SOHC, and it's just a completely different motor! The Evo ECU will do you know good because the fuel maps will be for the bigger injectors, timing maps will be for the DOHC 4G63. I sell Mitsubishis and I'm not new to them in any way. This would be like swapping a Evo ECU in a lancer ES. As far as compatability with the Immbolizer, I think it will be the same problem that warrtalon talked about, you cannot swap ECUs from evo to evo because of it, The same should hold true to any Mitsubishi with the Immbolizer. please let us know how it works out.
EDIT sorry about the name buthering, I was actually typeing a email to one of my customers with that last name at the same time. lol. Once again sorry about that.