kxxr,
I'm going to revise my date guestimate of your minty set.
The 1961 registration date for "Select Steel Tools" trademark is one of only a few solid date markers available.
The 1959 catalog makes no mention of "Select Steel" or "Indestro Select" tools, and it shows knurled sockets, probably of the Indestro Super era.
The 1977 catalog shows newer ratchets (enclosed round head and boxhead style) than yours and makes no mention of Select Steel or Indestro Select tool. So your set likely predates 1977.
So, given what little we can document, my revised date range estimate would be 1961 - mid 1970's.
Also, I suspect the original spinner handle in your set was lost and replaced by a similar, but earlier, Indestro Super spinner handle. They both look the same, have the same model number, but have different brand stampings on them.
Hope this helps some....