If you try it out, you have to let me know how it works! It's definitely an interesting concept. I would wonder how quickly someone would be able to run this contraption & also the depth of bite that the plate would make into the paper.
Oh yeah, FYI, you may have to sign up in order to view the articles at ReadyMade but it's well worth it.
* * * * * * * * *Another DIY letterpress guide is available on Instructables.com here, although from the looks of it, while it seems much less expensive to assemble, it will be more time consuming to print with. See below for the fully assembled "letterpress" and resulting wedding invites.