I know from past experience that the cam sprockets are very hard to get off the first time. The subie dealer tool is nothing more that a wrench the graps the sprockets teeth. The bolts are about 90ft lbs tight.
Somthing like this might work
Wrench
If that does not work and you are going to replace the valve cover seals, use a flat screwdriver on the inner cam gear teeth. It worked for me when I need to snap the cam sprocket bolt off.
Steve