To me this looks very typical for 1970s era military development work. Prototypes and sometimes test boxes would often be built with non-mil spec components. Layout is standard for Rubylith hand layout. CAD didn't take over until the 1980s. The drilling was definitely not done by some average Joe in his shop. Probably not CNC, but done on a mill or equivelant. Socketing active components was common also as the fab and test practices of people who grew up on high voltage vacuum tubes were not kind to semiconductors. And the jelly beans of today were still the prized and rare parts of recent memory. The box is definitely designed to be tossed, thrown and driven over.
Somewhere in a warehouse there is probably amazingly complete documentation of this device. Requirements, design notes, masks for the PWBs, schematics, test procedures and the like. Military contracts tend to be one size fits all so even the prototypes get the full production treatment. But the documentation might as well not exist because there is no way to retrieve it. No one knows where it is and there is no searchable index, even on paper.
Based on the serial number there were at least either 8 or 108 of these made. And probably at least one revision, hence the B series serial number. Which might also imply even larger numbers.