Mysterious Red Box - detail piece for ESB Boba Fett blaster stock

The Parts of Star Wars' Facebook page (https://www.facebook.com/PartsofSW/photos/a.528934313895854/1797009120421694/?type=3&permPage=1) uploaded an image of a part that has finally been discovered today. The problem is that the part is no longer produced, although there are clear images of it and even measurements for it from the manufacturer's catalog PDF. I tried to match these as best as I could. You are welcome to share and print this, and hopefully improve my model.

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