Tanning, especially heavy tanning to the outer cover doesn't always equate to brittle pages. What you need to be aware of when trying to work on a book like this is spine splits and issues with how you hydrate the book. I have personally pressed many books with heavy tanning and most of the time its fine, but every now and then something does happen. There is always a risk involved when pressing a book. Heck, we have seen lately that there is a risk involved when shipping, grading or even storing books.