Hi Mykeris,
Your post has started me on a quest of sorts

. I made contact with Abdul Razzaq Lubis, a Penang based researcher on Mandailing history and culture and by happy coincidence he turns out to a direct descendant of Tuanku Raja Bilah from the maternal side. He's even published book on Raja Bilah's exploits in Papan complete with the original letters and materials now stored in the national archives.
He runs a very informative site where I found some old pictures of Mandailing Rajas and their retainers:
http://www.mandailing.org/Eng/old%20...e-Hochzeit.jpg
http://www.mandailing.org/Eng/old%20...0Pekanten.html
Http://www.mandailing.org/Eng/old%20...%20gefolge.jpg
Some kerises can be seen lurking in the pictures, though I wish they were much clearer to see.
Basically the outward dress of these kerises look Malay or Minangkabau to me. Any ideas anyone?