Thanks for all the comments! I had a good time building it and I learned a few lessons in the process. I'm already starting to think it looks fine the way it is, but I'm still going to clean some things up before I call is finished.
I think the valve timing is like most other steam engines. The valve is at full travel when the crank is 90 degrees from the piston rod. Just had to play around to find that point.
As for being and addiction, I think that ship has sailed! I was hooked the first time a made a part on a lathe.
Eric