It is, and I figure I'll use the dimensions of that one to give me a good idea as to what would be a comfortable frame for this build. As to single-speed or fixed-gear, horizontal dropouts aren't an absolute requirement. There are other options for chain tensioning.

I'm really just looking for an excuse to build a bike, and as I mentioned above, there's no sense trying to duplicate what I already have, so I'm looking to build something that has a different look and feel, and given the kind of riding I like to do (I don't race, but like to ride long distances - there might be a century in my near future), I thought it would be fun to build something a little beefier than my roadie with slightly bigger tires, maybe some fenders. I also thought that going fixie or single-speed would allow me to avoid some of the expense of the componentry, still get it on the road, and have a chance to play with those configurations.

This thread has given me a ton of information and has been very helpful. Many of the frames/options suggested have led me down a few rabbit-holes that have allowed me to learn more about frame selection, considering I've never built up a bike before...