According to my cursory interwebz searching, Rystl was a consumer electronics company out of Florida. They started in 1970 and went under in 1986. I think they mainly imported Japanese produced items for their brand.
What little info I can find on their CBs suggests that Cybernet made most of, if not all of, their chassis. Which makes sense for the time period.
Your radio appears in Sams CB-99, if you can trust the indexes on the web. A crystal mixing chart can be found here:
https://www.cbcintl.com/XTALS/AM 37600-10180-10635.pdf
From what I can find, Rystl only had 4 models of CB. So kind of a rare bird there. That it's in such good shape cosmetically is a nice bonus.
And that's everything I know about it.