I showed off my paper-tearing contraption of at the 2013 Southern Graphics Council conference in Milwaukee, but it just received a new tweak. Something that I am embarrassed to say took me this long to figure out.
I switched out the clamps that normally hold the straightedge to drilled holes and wooden pegs. These make switching between two sizes much quicker. The new contract printing project, which uses two different paper sizes, made me come up with a solution that didn’t require me to remeasure every time I switched sizes.