I think the reference to 1947 is the doctor's interview for Project Paperclip, projected in the recreation hall in Return to the Admin Block. That said, Lesser Known Ecological Aspects of Humanity suggests MKULTRA took interest in pursuing his work in 1958.
I was wrong, there is no date on that film. I don't know where 1947 comes from. :|
As for when the Walrider was created, well technically it was created during the incident at the Asylum. The research is dated back to 1938 or earlier, but Billy is the only one who was successfully able to generate and manipulate nano particles outside his body.
The problem is that we don't have a lot of details about the start of the nanotech program. All the older documents are hypnosis and drugs. It's possible the Walrider didn't exist until Billy Hope, because the nanites are created from Billy's cells. Thats what it says on Morphogenic Engine anyway