Was Unibody Strengthened for Convertibles?

Hi,
I am making a list of topics to research for my '64 Valiant project, and I keep wondering about this. Full frame cars would have the rails boxed to compensate for the lack of a roof, but could the Unibody be rigid enough that it didn't need extra bracing?

thanks.
Jim O.
1964 Valiant Signet 200