You should be ok on length. I'm 5'6", short-waisted and all leg. You can see in the photo below that it hits me mid-knee. I'm guessing it would hit you slightly above the knee.
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I'll take a look at it when I get home this evening but I'm thinking it would be a pain. The skirt/bodice seam is not a straight seam, the skirt has pockets, there's a side zipper in the bodice and the skirt has pockets so it wouldn't be a simple alteration.
I also would not recommend running a 1/2 marathon in it. It is a comfy dress for park touring, Halloween costume, even to wear to work but the bodice can get warm during casual wear. It also has a layered skirt. It has the outer layer, a tulle layer and a 3rd satiny lining layer. There are some on etsy that look like they'd be better for running