As per current layout, page numbers and running heads are both on top of the page, numbers on the outside (outside = away from the spine) and running heads on the inside (= near the spine):

The problem: I will argue this is not good when you receive the book in print. When you flip through the pages (especially when the pages are ≃ 500) if is way better for the running heads to be on the outside (away from the spine). That way you do not have to fully open the book to now where you are and you can navigate it way better, especially when hunting for a specific section.

My suggested solution: put page numbers on bottom and running heads on top, both on the outside (away from the spine). I do not have it with me now but I think I saw this layout in my italian translation of Gnedenko’s probability theory book.