I ended up buying the stencil adapter as suggested. So far it seems nice, though my printer hasn't arrived yet.
Pros:
-Very nice machining
-Easy to adjust to different stencil widths.
-One pneumatic switch very securely clamps or unclamps the stencil.
-Two different sets of piston brackets were included.
Cons:
-The instructions are terrible. The pictures are barely visible, and show a different model of stencil holder. I managed to get it assembled, but it took longer than it should have.
-Pre-cut hose pieces would have been nice, or at least include the lengths in the instructions.
-Many of the metal pieces hadn't been cleaned after machining.