unfortunately its a lot harder then it seems...it is a different chassis code yes. the exterior body panels you can swap over with minimal modification.myself included have done this... the engine and drivetrain however are another hurdle to leap. as of current, there was only one person who tried it and was even nearly successful. however the project was dropped due to that same person just importing an 8g vr4. his user name is MANTE if you would lik to search his thread and see what he had done up untill the project was dropped to see what is instore for you.
the entire interior is much different as well the door panels, dash, seats and center console would all need a bit of work to be made to fit.
most of the people (with the i4) tend to either swap in an evo 5-9 (excluding mivec) 4g63 engines since they are nearly direct bolt ins...another option is to build the lower end of the 64 and just use the 4g63 dohc head...it pairs up with the eclipse 5spd tranny...for more info on this look up stewi, cali, and goosey2099 they all have a lot of info on the tranny swaps and engine swaps if you decide to go that route
if you are however dead set on a full conversion you are definately in for a lot of fabrication and it will take a while to complete, i did read of a mirage successfully swapping in a 6a13tt successfully but thats where my knowledge on that subject ends. i couldnt tell you whjat they did or where to even find the info