I started thinking, though, what did that original strip format look like? I wondered if anyone tried using Action Comics #1 to work backwards and see if they could approximate what Siegel and Shuster's submission looked like. It turns out, though, that we don't need to imagine it -- it still exists!
Before National bought the rights, McClure Syndicate tried shopping the idea around to newspapers, like any other comic strip. Naturally, newspaper editors weren't going to buy some totally new idea sight-unseen, so McClure printed up small booklets for their salesmen to carry around with them and show editors. Thirty individual Superman strips -- the month's worth of samples Siegel and Shuster had worked up, including a more detailed and gorgeously illustrated origin.
It was just a sample of a still-untried concept, so they weren't widely distributed. Nor were they realized to be of any value until some time later, so these booklets are exceptionally rare. There's only a handful believed to still be in existence, and they occasionally come up for auction.
So in case you're curious what the first Superman comic strip looked like -- before the character showed up in Action Comics -- here's the art that was shown from the latest auction I've seen for one of these...