Pretty much everything part related to the G&P upper receiver is compatible with only the G&P bodies.
Off the top of my head:
-Dust cover is of different length
-Charging handle spring attaches via screw (TM/Clones it attaches via a hook)
-The button next to the charging handle (can't remember name, sorry) is attached via a detent pin (TM/Clones it clicks in with 2 notches)
|