Well Folks, I deem the experiment a success!!!!!
While there is still a bit of trimming and fitting left, my Menards purchase appears to be working out.
While I never thought about the possible use of a window planter, I did find that the elongated window well cover had the right corner radius that I was looking for. I cut it down to the wheel opening and it fits pretty darn good. I did make one boo boo though, I should have made it a couple of inches smaller, but it's no big deal to cut a couple of inches out of it.