Bill,
Awesome work on the car!
If you reallllly want to have some fun with those plates AND you would never have to worry about the screw heads popping off....
Before you attach the plate, insert the shortend screws, flip the plate upside down and enlarge the end. (Like maybe using a center punch in the middle of the shaft??). Basically turning the screw into a rivet.
After you attacht the panel to the sills, the screw head could/would still turn and turn and turn and turn, but never come out!