The '48 manual shows both styles, while the '47 manual shows the installation of a u-bolt style onto a bike that doesn't originally come with one. I don't believe it to be later than 1948, because the kickstand moved to under the floorboard on the 1949.
Tom, how about a really late 1947 model H engine and one of the first 1948 frames? That would be right up Simplex's alley!!