That's fantastic! Thanks for doing that, and sharing it here.
Several of the things Mr Post mentioned struck a chord with me, as I lived through many of the things he talked about.
He spoke of the "show value" of his father's vinyl Universal Studios classic monster masks and selling masks to Disney, and I well remember visiting Disneyland in the 1960s and seeing a high shelf in the Magic Shop on Main Street with all the various vinyl monster masks displayed. I bought one, not a monster per se but the sci-fi/horror film character actor Tor Johnson. It terrified the neighborhood kids!
About the timing of the Star Wars masks, I saw the film in the summer of 1977 and knew that I had to be Darth Vader for Halloween! I can assure you that nothing was available at that time, so I had to scratch-build my costume. I was 20 years old, and at 6 foot 4 inches not Vader height but it would have to do. There was no internet, DVD, or even VHS to get screen shots from, the only available images were movie posters and fan magazines. I based my Vader mask/helmet on the only poster I could find, not a photo but a painting, which turned out to be rather inaccurate.