Jay, this project was on my list for last weekend but I became side-tracked with other things.
I'm hoping in the next month to build a barn-door tracker to mount on a tripod for my DSLR - so not quite Dob capabilities.
I've been doing a fair bit of reading lately. Here are some links I came across, so they may be of assistance to you also:
http://www.davetrott.com/DoubleArmBarnDoor.html
http://education.jlab.org/tracker/index.html
http://www.tucsonastronomy.org/barndoor.htm
I will probably go with the double-arm design and copy the dimensions directly from David Trott's page (why re-invent the wheel).
Regards,
Stephen