do you know if it is an L5 or an L7?


If it is an L7 those exterior dimensions would work very well for a box. It would leave you a little under 1.25cu after displacements.

If it is an L5 then it would be a bit large. It would be an easy fix though, just a matter of taking about 2" off the overall leangth of the box. You will end up with about 1.1cu.