I had the bigger platform and I have to say Ford's pictures are a crock for the bigger rack. The cross rails are either 27 1/2 inches apart or 54 1/2 inches apart. I tried to mount the larger platform with the mounts you have in your picture and it did not work. The rails/rack do not fall in the right place to match up. I had to return everything.
Now I thought about it again and I picked up Yakima Timberline mounts that go on the roof rails and mount the rack directly.
So my pictures show - that with the larger platform K - you have to have the crossbars 54 1/2 apart from each other for proper support. If you use the connection system shown in your post, the rack will not fit. The only way to make it fit is if the crossbars are 27 1/2 inches apart, which is way too narrow for the platform K. I mounted it that way to test and it was too floppy on the front and the back.