You know that we make a notch that's designed to match the contour of the 60-72 C10 frames. You can shorten the sides and top cap to be the exact heigth that you're looking for, and it will be super easy to install because of the shape.
Here's an image of the notch to give you an idea of the shape.
Let me know if you have any other questions, or think this will help you with your project.