Upgrade Metal Head

Highend Airsoft Upgrading?
I've been looking into an AEG to upgrade and i came across this one.
http://www.hitguns.com/JG-AK47-Beta-CQB-Short-Barrel-Airsoft-Electric-Gun-p/jg-0509mg.htm
* It has a metal gear box
*500fps .12's they say 380+ with .2's I'd say probably more around 425-450 if my math is correct.
Anyway would it be possible to put in either a M140/M150 spring in that AEG? I know I'd have to change the plastic bushings to metal ones right off the bat, a higher torque motor maybe, and a few other things reinforced piston head reinforced gearset and spring guide rod. I feel like i'm forgetting a part but anyway(i'll figure out where to get those later.)
Anyway question is it is possible to do such a highend upgrade on that JG aeg?
If it breaks the teeth i can always replace the piston. That kit is for a M120 I'm looking for more power then that. Especially as that gun is right around what a m120 kit would give me in terms of fps.
It might have metal bushings in it. It might break the piston teeth. You could just buy a kit.
http://www.airsoftgi.com/product_info.php?cPath=31_54&products_id=2972
I'm just saying it will save you money to buy that kit instead of individual parts and buy a 140-150 spring and the quality parts will upgrade your FPS as well as be more durable
you will need a 9.6 battery too.
A look at what is currently available on eBay
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