Swap out Plastic body??

[SuperCriollo]

Get a gun that already look the way you want, you'll save yourself headaches and money in the long run. Even adding a rail system might not be as easy as it looks. Removing the barrel nut can be extremely difficult sometimes, and you run the risk of breaking something. Furthermore, once you put the rail you are gonna have to use a fugly battery box, or rewire the gun to the back, and be forced to change the stock or use small buffer tube lipos.

[BennyBoy]

Receivers are hella expensive as well

[Stealth]

KA M4 internals are better than WE internals for what it's worth.

I'd spend a few more bucks and get a metal KA M4 to be honest.