Art Wallace got most of his information from the Mason drawings. He had an opportunity to see them in the early '60s. He's been researching Mason locomotives for many years, and is nearing completion of a book on the subject. Jerry Kitts may have had the opportunity to see much of the same resources as Art, and probably some others, but I don't think he's consolidated the information or prepared drawings like Art has (at least not yet). They are both great resources on the subject.
You can contact Art at:
aandgbwall@aol.com
and Jerry at:
jkitts@inreach.com