The motor cage is different between the AK and G36. If you're lucky, you'll be able to re-use the JG/VA one (many V3 gearboxes don't come with a cage included). The thing is, the JG/VA stock motor cage is probably one of the lowest quality components in that entire gun.
There are plenty of G36 motor cages on sale out there, if not continent-side, then at ehobby, KH mountain and elsewhere.
Now you know