[The Radium King]

the 2005 uses a 7.8 version of the computer so won't work with a 7.2 computer (ie, what was in the cars before 2002).

while staying with the old maf housing (and the associated restriction) isn't perfect, the 987 air box is a very big improvement over the 986 unit. the 997 plenum is a very big improvement over the 986 unit, and the larger throttle body, at the very least, improves throttle response (power comes an earlier in pedal travel).

regarding the question of tune, i'd assume that an aftermarket tune is the best, and there are a variety of options out there. at the least, running with an oem tune from a car with a larger maf housing (pre 2002 e-throttle 996) is the less expensive solution (1/2 hour of shop time vs $600 to $1000 for custom) and gets you what the 996 guys get.