That's about what I figured. Hubbard also bad mouthed Napoleon Hill.
I found this and the sequence:
Science of Getting Rich by Wallace DeLois Wattles written 1910
The Law of Success Course by Napoleon Hill 1928
How to Win Friends and Influence People by Dale Carnegie 1936
All three books built from the first. All three talk about the "ether", Hubbard renamed it "theta" or "theta body"
Hubbard was also an expert at rhetorical writing. I believe hubbard borrowed from Hill & Carnegie to set-up his Bridge. And of course was making it up as he went along and added things from other religions, psychotherapy, hypnosis, etc. And everything Veda posted above fits right in. All long and drawn out over a lifetime as Nibs said. Hubbard even admitted he compiled from other works.
One of the five canons of rhetoric is "inventio" or invention: the process of developing and refining your argument.
Hubbards "inventio" surely was invention in the art of developing and refining his bullshit wacky cosmos sci fi stories and convincing us they were all true. Somebody slap me silly.
Hubbard used rhetoric only in the wrong way, to entrap. Just like his "admissions" state.
I dunno, this is how I see it.
PS: This thread is loaded with information, links, and links leading to links leading to more links. Some of the links no longer work, most do.
It's sloppy and somewhat redundant, and some areas, such as that of abreaction (catharsis), are not covered as fully as they might be.
However, if one has the patience to wade through it, and its derails, and search its links, IMO, it's a pretty good compendium of actual sources for Dianetics and Scientology.