I believe any Corsair with a KD designation is a IV. The framed canopy was a feature of early -1Ds, and it seems like the FAA got a lot of them, so the canopy isn't a good indicator. I don't see the circular irregularity that you're referring to myself Andy.
I should note that the second photo in that group is a post-war Corsair, and a IV, so that may be definitive enough, I don't know.