ok, this would be nice to hear again from you. i´m also interested if they find your ancestor . my ggrandfathers uniform-picture looks like yours and i know that he must have been in any case at k.k. Landwehr in details maybe was Landesschütze-Gebirgstruppe (since 1917 Kaiserschütze) or Standschütze. i have all all details like the head and that the trousers where more dark-colored then the above .i think i will also ask at the archive to get the proof and also where he was stationed. and i also hope they have him in the files....
this would be a head of Kaiserschützen (before Landwehr)just like my ggrandfather has on picture:http://www.dorotheum.com/uploads/tx_ogkatalogebe
and all looks similar like on following picture the second person of left sitting on the ground:http://www.kuk-wehrmacht.de/img/oe1898_07.jpg