^ in GC its one either side of the Pitch mount on the firewall too. On GD I believe they are both pax side. The heating system is continuous flow, you can't just block it up or it fucks with your engine cooling (ask me how I know). If your current core is fucked it would likely be bypassed with a length of hose in front of the firewall. The feed should be from under the inlet manifold on the passenger head, and it joins back into the head crossover pipe under the manifold.

Once again, not super familiar with RS dashes, pretty sure in a GC you can do it with the dash in place but it would be a mirrion times easier with it out of the way

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MY93 Impreza GX 1.8L, 0hp, 0nm