I have one of these also. At first glance they look to be newer than the straight bar CWC Hiawathas w/ the Indian head badge. On the contrary they're older by several years (about 1940, Shelby built) and use the less attractive badge w/ the train on it.
I don't know what the Hiawatha model was called. Shelby used the name "Flying Cloud" on a few frame designs from the era, this was one of them. I haven't come across a Gambles catalog of the late 30's/early 40's to actually see this bike complete and original. I have seen several complete and original Shelbys in this design but have yet to come across a Hiawatha like yours in nice original shape, mine's practically a rat rod.
Caveat, again, I've been wrong a lot lately. Hell, it's probably CWC built like everything else.