I’ve read several books on the SR-71, including “Radar Man”. It’s rather insulting that there are so many claims that it was developed using “alien technology”. Building it was an inevitable progression of existing technologies, starting with the ME-262.
From the radar-absorbing leading-edge material and its geometry, to the fuel that was used, the material science involved wasn’t a giant leap and didn’t require “off-world” sourcing.
Skunkworks has hinted that the SR72 will be revealed soon. Although I’m really excited to see it, we’ll never again see another book written by pilots.