99 RS Chassis
06 Legacy GT EJ255 motor + VF39 + aftermarket stuff
04 STi Transmission
04 STi drivetrain
05 STi interior
04 STi ECU
1.) When buying a chassis, especially where you get snow don't settle for one with rust of any amount. Take the time and money to get a good chassis.
2.) If you're doing a GD era swap (Like I did) buy an entire car. With that said you might be better off buying a running fine STi, seems like the going rate for crashed STi's are more in some cases. I ended up spending about 10,500 in parts when a chassis/car would have cost me $9-10k and about a full weeks worth of time figuring out issues.
3.) Do an ENTIRE interior swap. It takes less time and is easier on the brain to just modify the GD dash beam than to rewire the entire HVAC system/gauge cluster. Plus the GD dash and HVAC controls are 10x better/better looking.
4.) For a legacy/08+WRX (non STi) engine the FPR is NOT on the fuel rail, it's between the engine and the fuel lines, it took me a week of figuring out why my Subaru wouldn't run, because I assumed it was on the rail like every other Subaru I've owned.
5.) Get ALL of the electronic manuals and read the manual instructions, so you understand the wiring diagrams in full detail.
6.) If your oil pan is damaged during shipping (if you buy your engine separately like I did) fix the oil pan BEFORE putting it in the car. If you do it after you just have to drop the subframe again.
7.) If you're doing a GD WRX or Legacy GT engine swap this is the easiest route when it comes to the ECU. Buy an 04-07 STi engine wiring harness and plug in all of the sensors, tgv, etc. Use an STi chassis wiring harness and then get an '04 STi ECU. Lookup the 3 or so wires to swap at the ECU plug and that saves time/money buying the key and immobilizer crap.
8.) If you can get an 05 drivetrain, this has the good bolt pattern and wheels are easier to find with the 5x114 bolt pattern.
9.) You can use the stock master cylinder for the upgraded brembos, I use it on mine.
That's all I can think of off the top of my head. Everything works and I've put about 15k miles on the car in one of the roughest winters MN has had in a while. Take your time, it took me 2 months to strip it, research and rewire the chassis. It may take you less or more time, the point is do it right and it'll work out.