In the absence of any install information, I placed the unzipped Special Objects folder in ..Documents/FS2/addons/scenery and that did not work.
So then I moved the scotland folder to Scotland South Project...\places and the scotland2 one to Scotland South 2..\places. That seems to have worked but I haven't had time to check everywhere.
There is some wonderful work being done in the community, and I greatly appreciate it - but is it too much to ask that the zip files come with a simple txt file saying:
Place this folder in Documents\ AFS2\addons\scenery\(whatever), along with another line giving the corresponding path for those with Steam installations?