I just completed Rays' Mill Engine #3, but in a vertical configuration. It has
a 1.25" bore and was scaled directly from the plans for the #3. I've built the
#3 in this scale as a horizontal and all parts interchange with the vertical
version except the bases. My motivation for the vertical was to make an engine
that would run at a slow speed and I'm quite satisfied with its performance.
You can see a video fo it running at about 30 rpm here:

http://www.youtube.com/watch?v=F2c9oPjSbW0

Photos of the horizontal and vertical versions appear in the folder Lancaster
Engines.

Cheers,
Phil