Yeah the new age bolts directly on to it. I'm not 100% on the classic it should have a small bit of pipe going into it with the DV on the other end ok by the looks of it I'm wrong :) guess it happens it might be more in the middle coming off the air intake by the looks of this.
Fitting Instructions for Classic Impreza’s
Fittment is very simple, your kit should have obviously a dump valve (DV) in it, a blanking plug and sometimes a new silicone hose to go from the DV to the intake manifold. The idea is to remove your old DV (RED DOT ON PIC). Make sure you note the way it goes on, there should be an arrow on your factory DV, this will come in handy if you ever wanted to go back to standard. Once removed you will see that the DV has 2 pipe connections x1 to the intercooler (BLUE DOT ON PIC) and x1 to the intake (GREEN DOT ON PIC). Your new DV goes to the Intercooler pipe (BLUE DOT ON PIC). Make sure that it is clamped to the pipe or jubilee clipped. The blanking plug in your kit blanks off the hole in the intake return pipe (GREEN DOT ON PIC). Make sure that it is clamped or jubilee clipped. Then if you have a new silicone hose just swap that for the one that went from the intake manifold to the DV on your factory DV (YELLOW DOT ON PIC). Make sure everything is tight and secure then go for a run and see what you think.