Well this is a driver containment area as well as part of the structure to keep the frame and driver protection in place. The braced area is where the drivers butt lands and where the lapbelt will end up attached to the main frame rails.
We started planning the new Bockscar after I went 246... my 228 record was nearly 100 MPH faster than the first record we set back in 1984 with the car.... we knew we were already pushing the safety limits... over the years we added and changed keeping up with the safety within the rules.... but we also were the original builders and always kept in mind how old the car was... and the repairs from past changes and incidents.
So we are trying to build a car for 250+... The old one stayed together for the 190 experience... a lot of the structure is bent, but nothing broke, our biggest fear that the car was rusting from the inside... at some point, I plan to dissect a few spots to see what we had. I don't plan to make a lot of the "mistakes" we made, most were correctable. There were parts of the frame and sub-frame that were drilled and tapped to attach parts, opening those to salt exposure... not our best ideas...
but we never expected to be where we are now, back then.
Pork Pie knows what we want to build and how safe we want to build it. If it weighs in a couple hundred pounds more than the original...
maybe I won't need to put the ballast back in.