Yes, you need to put their cages side by side so they can get used to being close to each other. I would also recommend each day switching their cages, so Gus is in Neo's cage and Neo's in Gus' cage. This will get them used ot having the other one's scent in their living environment. Then start sharing their bath dust. Let one bathe, then remove them, and put the other one in the same dust. This way they will start to smell the same. After you have done all of that for a week or two, then I would try playtime together. A little bit of aggression is normal. They operate in a dominance heirarchy, so they have to figure out who is in charge. They will probably chase each other, bark at each other and mount one another. Fur will probably fly as well. I would only cut things off if you see any kind of blood shed, or if one or the other stands up on their hind legs facing the other one and/or chatters their teeth at the other. Those are signs of angry agression and not just dominance play, and could lead to a serious fight.