Wouldn't hurt to talk to the guys over at Turnin Concepts. They track their subaru's on a regular basis and have had some really good finishes. They're also one of the best suspension vendors you will come across. Miles over at RCE (racecomp engineering) is also a good guy to talk to in regards to mods/desired result.
Is your son actually planning on sanctioned racing in specific rule classes or just recreational track days?