I have a foxface in a 75 and while it is a large fish, I think it fits fine in the tank. Mine was 3-4" when I got him and grew to about 6 with in a year. He is between 6 and 7" now. I have had him almost two years. Hope that helps.
BTW--They are a really cool fish and will probably quickly become one of your favorite. I say go for it.