This wraps the tale up. Difficult to read as it is i can make a couple of observations.
1 The depth of apparent first hand information is substantial and all wraps around the so called round wing which is certainly nothing of the kind. Thus i suspect that this book happens to be a history of the development of gravity control vehicles perhaps inspired by an off planet source during the second war and then placed under Joint USA Canadian and British control for rapid development. I suspect a comparable German effort was then folded in as well, mirroring then rocket work.
2 In order to maintain secrecy we also have a false narrative using nineteenth century hollow Earth speculations and a false German migration mythology that includes a mass of escaping Nazis. None of this is particularly plausible or practical. Too many people in too short a time had to simply do too much for it to be true. ( this trick was used by the Chinese 2400 years ago in order to make alchemy texts an integral part of Chinese mythology - arclein )
3 Separate the two and we have a clear allied research and development program continuing to this day that we have confirmed from many other sources. What is interesting is that most UFO sightings could turn out to be from this program. The provided power plant of 1943 would provide what is needed for small craft. Again it still demands that we know too much too soon about materials and that is something not readily done.
I discovered little in the form of new insights which suggests that such was carefully edited out. Obvious sections are missing and irrelevant sections sustained. All we get is a nod here and a hand wave there and insistence we simply accept plausibility. An initiate would be expected to read only those passages pointed out.
A history of gravity vessels was appropriate in 1975 as participants were beginning to die out. Releasing it forty years later ensured that no living witness could actually confirm a word. Add in the mythology and unless you are instructed, you will dismiss it all as bunkum and that was the whole point.