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you'll likely have seized up turbo flange nuts considering how old the car is. they will round off if you're not careful. I usually use a propane torch directly to the nuts until they are slightly red. Then they'll break free with hand tools. inspect the oil inlet pipe on the turbo, they commonly to fail near the weld point after a while. you can bend it out of the way to remove the old turbo as long as you're doing it by hand and making a bend in the center of the pipe; don't use pliers. bend it back to exactly line up with the inlet hole afterwards. the oil outlet hose that connects to the bottom of the turbo should be soft and pliable. replace if it feels hard when squeezing with fingers. when installing the new turbo, as caboobaroo said, the inlet hose can rip if you're not careful. i loosen the bolt holding the intake pipe so it could slide forward a bit, then wiggle the turbo in. sometimes when working with a bigger turbo that can't be fit with wiggling alone, i loosen the uppipe brackets and remove the exhaust header. that leaves the uppipe dangling and enough clearance to wiggle the turbo onto the intake hose. look up how to prime the new turbo with oil before first start of the engine.

It doesn't sound like your son changed the uppipe yet? it's not part of the catback exhaust. To reiterate what matt167 and wtdash said, please make sure the uppipe is changed to catless before changing to a catless downpipe. If this was done already, go ahead and change out the downpipe.

i've been in cars with dss carbon fiber shafts installed. all sti 6 speed, there is a noticeable humming on all of them on light throttle at certain speeds

black metal pipe stuck to the manifold? that's part of the pcv system. that back bolt is a pain. if you look from the top, the intake manifold splits into two runners leading down into the head. i've been able to find the right mix of socket and wobbler extensions to poke in between the two intake runners and bend downwards to reach that bolt.

roll pin can be tapped out from either direction. when you put on the new axle, get a bright flashlight and shine through the roll pin hole from behind. make sure you can see a perfectly circular hole before tapping the new pin back in. if not, pull out the cup and flip it 180deg and put it back in.

one of two the camber bolts is eccentric, you'll have to loosen from the nut side instead of the bolt side.

I've had good luck finding odd hose leaks by pressurizing the coolant system. Warm up the car, turn off engine, pull out the overflow hose from the tank and put about 10-15psi into it. Ive found failing hose clamps around the heater hoses and turbo reservoir this way. Was chasing the problem for months after the engine rebuild. Car doesn't overheat, no bubbles in system, it just starts losing coolant between fillups. For my case, coolant would sneak out the heater hose clamps on the firewall. Which was where I disconnected them when pulling out the engine.

take off both accessory belts and start the engine again. hopefully the noise goes away meaning it's one of those pulleys like you suspect. if there's still noise it's likely a timing belt idler going bad and needs to be addressed immediately.

You could convert a 5mt to 2wd by replacing the center diff with a spool lock. VW guys have been doing this for years.

swapped blowers on my 2003 impreza wagon with a 2006 year unit. it looked like the motor is molded into the ducting assembly. i could be wrong though, didn't look too carefully as i already had the entire assembly and didn't need to swap blowers. anyways, to get it off of the car, I had to remove the nut holding the white upper piece to the dash. (it's hidden under the wiring loom). then when all nuts are off, the white piece is held to the black piece via plastic tabs. you should be able to feel them and unclip them by hand. after that you should be able to pull the lower assembly out.

Quick search on ebay shows that it's the same bearing for 1993-2007 imprezas. (non sti) http://www.ebay.com/sch/i.html?_odkw=wheel+bearing+impreza&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xfront+wheel+bearing+impreza.TRS1&_nkw=front+wheel+bearing+impreza&_sacat=0 The manual likely is trying to say that the bearing isn't reusable. Once you press it out of the hub, you've already ruined it. Press in a new one and you're good to go. You'll probably need the grease seals as those easily get ruined when pressing out the old bearing.

If you suspect the fan motor, I'd remove the glovebox to get to the fan motor connector. Test for voltage on there. If there's voltage, chances are the motor brushes are worn. This happened on my impreza, the fan would intermittently work. Once it started spinning it's good until shut down. I eventually swapped in another blower unit and things were back to normal.