I have a mount that is a clone of that deer Slider. My grandpa shot it in Oregon, it's a 3x3 and is missing the same back tine. It measures 39.5" wide and scores about 175". I do think the one you found might be a tad short of 40"...but that's only a guess from the supplied photos. Maybe someone will shoot him and we can figure out what he is. Nice find.
shawn