the legacy and imprezza pedal boxes are not different at all. I have found some differences with the hydroulic series between models and years but they are all the same in basic dimensions.
Wiring for neutral- You need to use the all black sensor on the imprezza/legacy pedal box. You must run two wires, one for each pin on the switch. These two wires must run to the transmission harness that attaches to the inhibitor switch on the pass side of the auto. Here you will find 4 wires in a row. One wire will be black w/ yellow stripe, One Blue w/ white stripe, on Green w/ red stripe, one Brown w/ a yellow stripe. The wires you need for neutral will be the blue/white and black/yellow. You need to run 14awg wire from the pins on the switch(on the pedal ass.) to the black/yellow and blue/white wires. This will allow you to start the car only when the clutch pedal is depressed and will kick off the cruise when the pedal is depressed.
Wiring for the Reverse lights. First you need to locate the reverse switch on the trans. Now having done a ton of swaps I can never remember/pay attention to which is reverse and which is the in gear switch on the trans. what you need to do is get an ohm meter and measure continuity of both the switches. The reverse switch will only show continuity when in reverse and no other gear. The in gear switch will show continuity with all gears inlcuding reverse but none while in neutral. If it is an older model tran (4.11 cable style) the color of wires are usually red and red/white. You need to run an 18 or so gauge wire from each of these to the same harness you did for the neutral switch. The brown/yellow and the green/red wires will be the two you need to connect the two reverse light wires to. This will allow the reverse lights to illuminate when in reverse only. If they illuminate in all gears, you hooked up the wrong switch.
Hope this helps and sorry it is so long winded. I also apologize for the delay in response as I have been taking a bit of a vacation before I begin student teaching tomorrow.
Tom