I think as the site has matured and grown in content volume, some original links no longer work, some rearrangement has also occured. Otherwise, you should always be able to find stuff at docs.khadas.com in the relative model section.
Case fasteners on the original acrylic case are M2(a.k.a. 2mm). If I recall, they are 20mm in length, but I will check it tonight to confirm.
In this thread(scroll to bottom of the first post) you can see the case sections and fasteners.