Yes, but I believe the plans the museum has are copies of the originals at the Maine Archives. You can order copies for yourself.
Bob Jones' book had material lists for some of the various freight car orders W&Q/WW&F purchase from Portland Co. The material lists do show the dimensions of the center, intermediate, and outer sills as well as dimensions for the end beams; in fact, all the dimensions for every stick of wood on the cars. There are also dimensions for the various bits of steel, wrought iron, and cast iron, too.