2001 AT here, just had to remove and replace mine here recently and this is how I managed to do it without buying the tool. On removal I used the old belt that was going to be replaced and gripped it with vice grips and spun the motor enough so the vice grips lodged against the bracket for the AC compressor (crappy solo technique). On installation I had to do a little better and realized if I put three 3 inch 3/8 socket wrench extensions in the holes so I could use a long wrench with a cheater bar to prevent the the motor from turning while I could get the bolt torqued to the 130 ft lbs torque it calls for. I had to put the socket on the bolt, slide the wrench in to prevent turning, then attach the 1/2 drive extension on my torque wrench to the socket as the socket wont fit in the gap after the holding wrench is in place. You will need a friend with a little mass or strength for the holding part IMHO. Mine had normal RH threads btw.
The Subaru part number you have is correct for my vehicle, 499977100 , unsure on the specs/cost though.