. Oil Catch Can
. Legmaker True CAI
. Fastman Ported Throttle Body
. Catback (Your Choice Brand Get a True 3’)
. Unlock PCM + Handheld (Tune it with Jay Greene)
. Kooks LT 1 7/8 Headers
. Kooks Catless or High flow mid pipes
. Cam it
And with all these mods in place you’ll be past 500
Since a stock scat pack probably dyno's in the 420-430 HP area (depending on the dyno and other factors) I'd say he needs to do enough mods to pick up at least 70 HP. To get that kind of HP I'm thinking a 75 shot of nitrous or super charger.
It's kind of tough to pick up those kinds of numbers with just some bolt on's. Now if the OP meant he just wants to bump the stock HP from 485 to 500, then the bolt on's and/or a tune would get you there.