I posted some tips on timing belt replacement about a year ago when I did one on my 2.2 liter 98 legacy. There were a few responses to that with additional advice, and I think it is a good thread. This past weekend I did my 2.5 liter SOHC 2004 outback. Here are a few things I learned:
The crank pulley has a hash mark on the BACK of the pulley. Any marks on the front are meaningless and will only lead you astray. I initally set up my belt's marks with the two hash marks on the front of the cam pulleys and the dot on the front of the crank pulley. This was 90=B0 away from the hash mark. If I had started the engine like this it would have been certain disaster. Fortunately I did an idiot check and tried to turn it over by hand first. When I felt resistance I knew something was wrong and looked at a youtube video concerning a 2001 forester TB replacement.
Turning the engine over by hand using the camshaft bolts doesn't work. I did this and wound up having the belt skip two teeth on the crank shaft. I thought I had a defective new tensioner and started cursing since it was Sunday afternoon and no Subaru parts places were open. I put the old tensioner back on and tried turning the engine over with the passenger side cam(which woudl be less likely to make it slip teeth since it puts more of the blet under tension) It slipped at the crank again. I had been using the cams since it takes more torque to turn them, so I figured I'd do les damage to valves if everything wasn't assembled properly. Afdter talking to a professional Audi/VW mechanic friend of mine, he confirmed that many engines will slip teeth if you use the cams to turn them, and that I should use the crank only. I reassembled it with the known good tensioner, cranked it with the crank, and it was golden. So then I took it apart for probably about the 15th time(seriously) and put on the new tensioner.
So what I learned in my 15 or so times of taking the belt off and putting it back on: The order that you take the tensioner and idler pulleys off is critical and makes all the difference!! I can't stress this enough. When taking it all apart, line up your marks to the block, then you can actually press down on the TB just to the right of the tensioner to make the tensioner wheel go up, thereby alligning the tensioner holes, then stick your allen wrench in there. Next you first take off the bottom left pulley. It is the bottom smooth pulley. Then take off the toothed one by the water pump. Now you can get the belt off.
When putting it back together, bolt the tensioner to the block, loop the belt through the crank pulley, tensioner, drivers side cam, water pump, and passenger side cam in that order. Push down on the bottom of the belt to keep tension on it so teeth don't slip anywhere. Then put a breaker bar on teh passenger sid ecam and nudge it a little CCW to put more slack into the bottom of the belt. This will amke it much easier to put on the toothed idler pulley. You must put that one on first!!!. Once you get the toothed one on, then put on the smooth lower idler pulley. If you put the lower smooth one on first there will not be enough slack in teh belt to get the toothed one on unless you have superhuman strength and luck.
Also, I agree with Steve that you don't need to take out the radiator. You do need to take the fans out though.
I used the trick of putting a breaker bar on the crank bolt and tapping the starter, but instead of putting it on top of the frame rail by the battery, I put it 180 degrees from that so it hit the bottom of the frame rail on the passenger side of the car.There are no fragile AC lines or transmission fluid cooler lines or batteries there. Much safer.
Good luck