i would think that finding an f40 out of a g6 would be the easiest. lots of work for not lots of reward. you are going to have to be real nice to it or suffer the consequences. on the brighter side you can still get a quaife diff for it.
Is the diff the only weak point though? I put a Quaiffe in my Stealth after breaking a few diffs and played a little too hard once and ended up breaking 2nd gear. I guess since the diff wasn't going to fail/break that something else did.
2011 Mitsubishi Lancer GTS - DD mode
1991 Mitsubishi 3000GT - Many mods to come