I did an X2 UI mockup in a hidden thread at least one years ago, may be two. Here it is.
I was also proposing a slightly more flexible secondary scheme, so you'll see three tools instead of two. That was before X2 reverted to backpack.
Otherwise, I hope it would be pretty intuitive. It may be too late in the development cycle to revamp now, but for what it is worth:
(Click to Enlarge. Image is 1920x1080.)