http://www.subaru-svx.net/photos/use...svxfiles|23592
There are many vacuum lines and hoses under the intake manifold, and it is not that easy to remove and reinstall.
The rear anti-nock sensor is on the drivers side as the link shows.
A pair of hemostats, a good light, and an extra pair of hands is helpful.
If you remove the alternator you can reach the IRIS check valve and hoses.
http://www.subaru-svx.net/photos/use...svxfiles|24710