Q. Dear Donia,
A. Dear Len,
The best way to proceed is to consult a conservator. Boxes, being three-dimensional objects, are tricky to treat without some training and access to helpful materials. Luckily, you are in an area that you have relatively easy access to conservators—especially in the Cleveland area.
To find a conservator who can help you, you can consult the American Institute for Conservation's "Find a Conservator" page. Simply put in your zip code and select a specialty (in this instance you would pick "Book and Paper"). When I put Mingo Junction's zip code in, I found five conservators who could potentially help.
Good luck with your project, it sounds like a fun one.