Chris,
I believe the sills were purchased in Maine, and that they are fir.
The end sills, queen post timbers, and the wall studs were sawn by Dean's sawmill in NH - from oak logs that were cut on the museum's property.
All 18 pages of this thread, as well as the thread marked "Turner Centre Creamery Car" (I think) pretty well chronicles the start to finish of this project. There are still little things to do to make the car complete; we still need to install the brake system, including the brake staff and brake wheel.
Dave Crow