Thanks so much for your comments and photos - together they provide a very informative guide to the cords of early Jensen engines, very useful for anyone interested in dating the early models. Mine clearly has the late 40s type of cord, so maybe the cord was replaced at some point? The engine shows very little signs of use (especially the boiler), so I have to wonder what happened, if it is late 30s, as everything else suggests. At least it does match one of the known early types of cords. I could post a better photo of the plug, if that might help also.
Another question I have concerns the color. I read on one collector's website that the sky blue color was only used in 1936-37, the story being that Jensen found a quantity of that blue paint to buy at a bargain price, and since it was during the depression, they were trying to save money every way possible. Once it ran out, they switched to the darker blue! Any truth to that story, or any further information regarding dating Jensen engines, based on the sky blue paint color?