Most plastics of the era would not meet requirements for aviation fire safety, they produce toxic smoke when burning (still a significant problem today). There'

Most plastics of the era would not meet requirements for aviation fire safety, they produce toxic smoke when burning (still a significant problem today). There's an obvious tension between "reduced weight" and "not using plastics," but that was kind of the deal in aviation technology at the time. Aviation equipment is still pretty chunky today, because of the materials needed for low/no smoke evolution and vibration tolerance. Considering it probably also had to meet a MIL-STD environmental spec, stripping a commercial printer and putting it in some kind of aftermarket metal chassis seems like a much more expensive/higher risk route than using something that was already made to those standards. Environmental specs, in this context, usually mean min and max operating temperatures and acceptance of vibration and shock, within certain G-force and frequency measurements, with "without malfunction" and "without damage" thresholds. Aviation and military equipment have to go to environmental testing laboratories to be certified to these requirements, which can be a considerable expense on its own, and another reason it's smart to use an existing design. Besides, the military already made use of teleprinters in aircraft and so there was operating experience to build confidence. The space shuttle model is based on the family made by MITE, which included airborne variants used on bombers for example.