Boy Tim, you jinxed yourself in post 54 saying the 35mm versions worked.
I had read this by guitar Ted (a well known gravel bike bloger and test reviewer)"
several brands use "...UST based dimensions on their tires and it is a well known issue that these brand's tires do not work well- or at all- with Stan's based rims, which American Classic rims are based off of. Sun/Ringle' tubeless rims also use a Stan's based design/dimensions for tubeless rims, by the way.
So, if the Schwalbe G-One is based off a UST dimension for the tire bead, it would be no wonder that it doesn't fit the American Classic rim well, because they base their design off a Stan's dimension. I cannot confirm that Schwalbe is using this UST based dimension for their tire bead design, but it sounds like they are.
This is the trouble with tubeless tires at the moment- There are two major competing rim designs and tire manufacturers that either buy into using UST or fudge it so that they fit more rims than UST based ones. Some rim manufacturers shoot for a middle ground as well. The tire and rim folks are not going to freely share info regarding where their products fall in terms of fit either because that limits sales, which they are loathe to risk doing. Although some publicly do post this information, it isn't industry wide. Meanwhile, the consumer is left to sort it all out on their own dime."