Internals:
-m140 spring (or whatever he wants)
-neo torque motor (SHS, JG, Lonex, element, etc)
-SHS 15 steel piston
-SHS ported aluminum piston head (helps with transferring energy for heavy bb's)
-recommend switching to XYT or GE 18:1's
-recommend switching to nice 16awg wiring
-recommend switching to steel bushings
Hop up:
-prommy or madbull 6.03
-g&g green, madbull blue, or systema bucking
-pcs nub
There are a lot of different combinations for the hop up. If you feel up to it, I would recommend ER hop with EM nub. Next best thing is flat hop. Your call.
Basic DIY:
-shim via bevel
-install deans
-grease
-correct AoE to 12 o-clock with 70D sorbo and neophrene pad
-airseal mods
-barrel stabilization
-shim hop up arm
-etc...
Hope this helps.