I've heard that the STi's front and rear limited slips will fit a Subaru of like vintage. Is that true? Also, can I run the limited slip center diff in a Gen. II Forester with an auto transmission?

I took our '03 Forester off roading not long ago (yes, I know, I'm an idiot). It did fairly well, but when I got to areas where suspension travel forced me to lift a wheel off the ground, all the power went to that wheel (damn open diffs!:thumbsdow). I'd like to be able to wheel it a little harder, maybe eventually make a 2" coil spacer lift, trim the fenders, and run a more aggressive tire.

Speaking of tires, yet another question: Our Forester is a 2.5X with rear drum brakes. I want to run a set of 31" tires eventually on it, but the problem is that most 31's are made for 15" rims. If I wanted to keep with 16's, my tire choice would be limited. Clearence looks tight with the factory 16', so I'm pretty sure 15's wouldn't clear the front calipers. Am I right?