Replying to Subaru help please!

Hey, I realize this is a long shot but I figured Subaru's are common enough in the ski community that it was worth a shot. Here is my story, Vehicle is a 2001 outback with 135,000 miles

Last week on my way home from Beartooth I was headed up a hill, accelerating. I was in montana, on the freeway so I was going almost 90. Engine started to click, then louder, then died. I pulled over turn over engine, makes loud clicking, no start. About an hour later get it towed, try to start again, it makes loud clicking and will start and run for a little if I give it gas. I get it home, try to start, it will start and run but makes horrendous clicking. Have buddy who know Subbies come over. He thinks it is timing, we pull timing belt, it is missing little guard to keep it on the main gear. replace timing belt, still makes noise, think it may be coming from passenger head so we strip down to that and pull the head. I water test the valves, two of them leak, "good" I think " that is the problem" We replace head (My buddy has a lot of parts) and try again, still the noise... Not good! We try to analyze source of noise, seems to be coming from all the power transfer stuff that hooks into the back of the engine. That is not good news since neither of us have any experience with that part.

Now we are stumped, I am planing on towing it to a mechanic on monday but if anyone has any ideas what this could be it would make my day.

Thanks NS!