Na, he has a Lancer GSR, not a Galant GSR so he can use his existing GSR engine loom with an E6X and GSR patch loom no problem to run a VR4 4g63t engine. I've done it before as per the 4G63T into GSR tech sticky, and even used a Haltech E6X for that conversion (That GSR btw now pulls 326kw atw after Micks Motorsport had a tune of it).
Anyhow, htgsr is correct. The GSR ECU will run a 4G63T engine but not very well... just good enough to get up and running and drive the car about... been there and done that years ago. An EVO ECU will be better, but a Haltech E6X with plug and play better again considering he's looking at future mods and tuning.
Stick with it mate, every now and then an E6X comes up on a forum or EBay cheap. Last one I saw sold with an EVO patch loom for only $750!!! But the bargains are few and far between as they get snapped up very quickly. Budget for a few hundred bux more.