Family heirloom traveling desk/secretary

Wood (oak?) cabinet containing 6 pull out boxes. Overall dimensions 28"x15"x18". Boxes labeled as 'Receipts', 'Orders', 'Letters', 'Invoices', 'Bills' Lading Freight Bills', and 'Price Lists'. The cabinet does not have legs. I have it sitting on an antique table. There is a pull out writing board below the boxes. The third photo is one of the boxes open. The fourth photo indicates the manufacturer of the paper indexes. (Note patented 1877) The cabinet may have been manufactured by them also, as the indexes fit so well inside the boxes. I searched, but could not locate any manufacturer marks on the cabinet. My online research provided information and a drawing of the box on the 'Early Office Museum' website, but nothing on the cabinet. I have not found any photos of a cabinet that resembles this one. One ancestor was a contractor who worked on railroad construction in the late 1800s. He traveled often between Kansas and Colorado. From the labels I deduce it was used by a salesman. I do not know what to call it.....traveling desk, secretary, filing system????