i don't see why you would have issues they are not from the same genus so they should not show too much aggression towards each other, the issue is that some people do not provide their tang with the proper diet, if they are fed well and fed A LOT they should not be overly aggressive. also aquascaping plays a role, if your 120 is full of rocks and there is not much swimming space then some aggression may occur. usually territorial tangs will only show aggression towards competing fish (in other words fish that are of the same genus, or fish that are of the same size)