Did we have a large active General Schedule (GS) payscale then? I don’t know.
I don’t know either.
Probably not as big as now. I wonder why you wouldn’t just bring these experts in as GS or Excepted Service appointees, maybe even as terms so they don’t have the expectation of a long-term job. At my place the military folks work for the civilians and vice versa just fine. Each side has to learn the others’ rules but that’s not too complicated.