Single cam or dual cam? I can't remember when they stopped using the single cam motor.
I've replaced head gaskets on both. My suggestions, stick to subaru parts. Subaru sells a full gasket kit that has everything you need to do head gaskets, literally has every gasket and seal that you'll touch doing that job. Buy that kit, your life will be so much easier. I'll try to find where I bought mine.
Take the motor out of the car. Dual cam cars kind of require it. Single cam cars you can do in the car, but man it just sucks. Like really really sucks. I wish I had pulled the motor when i did the single cam engine.
If you have a dual cam car, you need the cam wrenches, because you have to remove the cams to take the heads off. They're like $50 each and you need two variations. I own them, and could loan them since you're listed as boston area. Trust me, they're worth it over trying and failing other methods.
If you don't already have the factory manual grab it. They're all over the internet, or you can pay subaru for access to their technical site and download it.
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