G&P Make Excellent armalites.
They are fully upgradeable, both internally and externally, though, they really don't need it. (maybe a shim job)
One note, G&P's have 14mm+ thread on their outer barrels instead of the standard 14mm-
This is really only an issue if you want a silencer, or different flash hider, and even then, 14mm+ versions are available, though usually with less selection, and more rarity.
It's better to light a candle, than to curse the darkness