In a normaly configured arrow, I find it challenging to stuff everything in it with a 3S 850. (ESC. Battery, Aura Lite control board, wires, FPV camera and transmitter). I think a 2S 1200 is about the same size as a 3S 850 so, size wise, it might fit. Check the dimentions against a 3S 850.
It will be interesting to hear if it makes enough thrust to fly reasonably well. The Arrow is very nimble but, all that twisting and turning bleeds energy. It would be interesting to see if a 2S can keep the momentum up enough to still twist and turn.