damn this is looking good (even if it is yellow!)
For circuit you won't need an enormously strong diff as it's not under the shock loads of a drag car. But LSD is a must. I'd avoid a locked diff in a small car like the lancer, they are twitchy enough as it is.
Whatever diff you use you will have to cut down anyway. The lancer is a damn narrow car. Have a look at what the datto 1200 guys use.