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Looks like we got us a Envoy! Assuming that Jim Mamoulides knows his stuff, and we know he does: http://www.penhero.com/PenGallery/Eversharp/EversharpEnvoy.htm

She has a couple of small dents not visible in the photos, a brassed spot on the top of the cap that you can see in the two middle photos, a twisted and solidified sac (that I was able to break apart and salvage the breather tube), and a 14K gold nib with a fair amount of flex to it. Not bad for $11, including shipping, two more pens, and a nice old Autopoint pencil.

Edit:

Well crap: the pressure bar is broken, but it looks like a Skyline type, so shouldn't be too difficult to source.