I know a guy who did similar with an old 75g to make two seperate tanks.
It seemed to work fine for the years he used it, but the glass was pretty thick compared to some of the 55g's I've seen made today.
You may want to look into the glass thickness typically used for the size tank your project is being coverted to. (Sounds like you may be going from 55g to 75-90g for example)
GARF's Tank Calculator may help some on those details.