Rocker Panel Construction

This picture is of a left side 1965 Dart rocker panel looking forward. It clearly shows the extra reinforcement member used in convertibles. Maybe it will help someone.

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Thanks!
Just curious if anyone knows how these are put together?

Looks like it's a big beam that is made to fit snugly inside the rocker assembly, but is not directly welded to the tortion bar crossmember or rear subframe assembly like subframe connectors are. So it stiffens the standard rocker assembly from the inside, and then they used the same rocker assembly stampings they used for the 2 doors?