Amendment for WRX
While the assembly procedure is similar for the WRX, the following images show how the fuel lines are routed differently. The Flex Fuel Sensor will go in-line of the return line, and the Fuel Pressure Sensor will go in-line of the feed line (if purchased).
The WRX Uses the lower connection (pictured) for a return - connect the barbed hose (no quick connect) here
The upper quick connect on the manifold side is used for either the fuel pressure kit, if purchased
The bottom connection here is the return line (shown bending down to the fuse box), which will be used for the ethanol content sensor (in-line of the return flow)
Below is a completed configuration using R&D components: