This step is pretty straight forward and simple. All the Classic pieces fit nicely and the rocker rail was no exception.
The rail was test fit into position against the remainder of the old one...
Once satisfied with the fit, we attached the new rail to the old one with three sheet metal screws to position it, then removed the screws and the rail and slathered the adhesive/sealant that came with the torque box from Classic to the old outer rail and the floor of the car where the "C" channel from the new rail would go.
The new rail was reinstalled and positioned with the same three screws in the same holes, then the rail was riveted in several places to the old rail and to the floor of the car from the inside and to the front of the rail through the wheel well.
One additional advantage of the Classic multi piece torque box is that this outer rail is now attached to the body with essentially a "T" section (original rail "C" section and new rail "C" section are opposite of each other) which makes the whole assembly much stronger.
At this point, we made the observation that torque boxes on these cars might be over kill. The doors of this car fit exceptionally well and open and close like new. This was/is the case with the rusted out box, with NO box, and with the new box. The car was originally ordered by and built for Mr. Morrison who was the founder and President of the Moulded Fiberglass Body Company...the company who built the Avanti bodies for Studebaker and the Corvette bodies for Chevrolet...so it may have received special attention. But, if you are counting on new torque boxes to fix sagging or ill fitting doors you might want to look for other causes of these problems.