Can i keep two young arowanas in one tank?

i got a green arowana as a gift from my boyfriend, now my aunt got me a RTG which will arrive in a week. my green aro is about 5" and im hoping that the RTG would be just about the same size.. I have two 75gal tanks 1 has my green aro in it and the other has a 16" aligator gar. i wouldnt want to put one of the aros with the gar cause for sure it would end up being a snack. so i was wondering if i could keep both arowanas in one tank?