ok first of all slow down a little
from what i no and have been told,
1. for intake go a monaro or hsv lower airbox (top is the same) with the second hole, as for the k&n panel filter i cant really justify the price of them for the gains but thats just my opinion.
2. ive been told that the alloytecs work best with a 2.25 or a 2.125 inch twin exhaust but same design as the gen111's exhaust, you will find a million 2.5 inch dual exhaust but there all designed for a 5.7 ltre so ive been told there too big. as for mufflers the go seems to be two straight the mufflers in the middle and the rear really depends on how loud you want it.
as i said before this is what ive been told from many people on this site and after a hell of a lot of ringing around this is what seems to be the go.