Next we spot-weld the new inner sill to the new floor panel, then coat areas that will be enclosed. Most people don’t know this, but at the factory, this is all one continous piece of steel sheet – only in the aftermarket restoration of these cars is the floor and inner sill seperated into two pieces. For strength, we will attach the inner sill to the A and B pillars with plug welding instead of attempting to spot-weld the new panel to the old, tired flanges of those pillars.