The cross sill just rearward of the front one does not require the plates since the bottom of it does not contact anything. It is a floater.
New cross sills all probably come with the plates, but I don't believe that the original floater cross sill came with them.
Having stated that, far be it from me to steer you away from Brad Allen's opinion. He is a great source for hard to find details (and I may need to buy some hard to find parts from him and I do not want to jeopardize that
).
Carl
