It goes here, aft of the intake manifold and above the front of the transmission. In the donor car, the firewall would have been close to the intercooler right where my hand is. This makes installing an intercooler in a WRX a complete pain - but in the kit, having all the space around the back of the intercooler makes things much easier, as I'll show you later in this post.
This is why it's easier to install the intercooler into the kit than a WRX - with a firewall in the way, the inlets are completely inaccessible, so they have to be bolted up before installing - and this leaves you trying to line up and connect to the turbo outlet and the throttle body at the same time, at right angles to each other. The folklore is that this usually requires lots of effort and swearing. Here, though, I'll be able to just connect to the throttle body and then bolt up the inlets. There is a load of space, so it's no challenge at all.
But I can't install the intercooler yet. Once it's in, getting to anything else on the top of the engine gets astronomically more difficult, so I have been spending extra time and care on being sure that everything else in that area is complete. Notably, this include PCV - positive crankcase ventilation. This is a requirement for emissions, so that blowby gasses and oil vapor don't just get vented to the atmosphere - they get recirculated into the intake and burned in the engine. The PCV valve itself is buried in that dark spot under the throttle body, so I have to finish that before I can button up the intercooler.
I had hoped to finish that all this weekend, but I didn't have the right sizes of hose to get the PCV valve installed for good, and I could not find any locally. But it's all ordered, and will show up soon.