Grinnell Brothers was a Detroit-based firm established in 1872 and remaining in business through the late-20th century:
http://historicdetroit.org/building/...s-music-house/
According to Mike Longworth Martin also made some proprietary models for them under the Wolverine name (most likely before 1930 TMK); by the time this one was made they probably switched over to Gibson as they were able to provide both flattops and archtops (although Martin did produce the C-/F-/R-Series archtops, they were generally not well-regarded then or now). Size-wise it corresponds to Gibson's period L-30/L-37 models (as well at the prewar ES-100/ES-125), and if the truss rod is in fact original (the Philips-head retaining screws are not, BTW) it's virtually unheard-of in a contract instrument; that said, one has to wonder why the present owner is unloading it for
substantially less than the original purchase price - and why the first seller fitted it with what appears to be a an Asian-made TOM-type bridge (total tone-killer FYI) when a proper wooden one could be had from StewMac for around $20. IMO you've got another dog here - I dare say there are other issues I can't discern from the pics - and quite frankly I wouldn't waste my time/energy/gas money even giving it a second look...