Touring GT sills

[Todd Drysdale]

Hello ,
Can anyone tell me what the underside of the rocker panel or sill is supposed to look like?
On my car, the space between the rocker panel and the steel floor is covered by a flat sheet of aluminium
about 6 inches across that is riveted to the underside of the rocker panel. This piece of sheet aluminium reaches from the rear wheel opening to around 4 inches into the front wheel opening.
I have a feeling that this is an old repair to try and cover up the rusty floor. It just looks too shabby to be from the factory. If this is the case , how is the underside of the aluminium rocker supposed to be finished and how is the transition from aluminium to steel floor panel made.
Any input is appreciated,
Todd