Thanks doc That is a "Tek-lok" belt clip (first time I've used one), and yes, it could be adapted to vertical carry just by removing the 3 chicago screws and rotating the clip 90 degrees. It's a very versatile attachment, but they're not cheap, running around $20-$25 each. Those rectangular shims inside the clip can also be adjusted for different belt widths as well.
I forgot to mention, the inlay on the arm guard is dried beaver tail skin.