In my previous life as a naval officer, we’d announce BRACE BRACE BRACE over the PA when a (simulated) missile was incoming. We were then supposed to hold on to something, anything, to steady ourselves for the impact; although the logic of that was somewhat questionable on a teeny 200ft, 600ton gunboat since there wouldn’t be much left. Nevertheless, Titanic Jack certainly survived a few minutes longer because he was holding on to something.
Different context here, but the same principle applies: bracing happens before the stress hits. So before cutting into the roof, I needed to install an extensive anti-roll structure to stop the car from twisting post-cut.
Green 3-axis construction lasers are awesome so I borrowed one from work:
This allowed me to keep the bracing positions symmetric across the car (which would also define the plane of the new rear bulkhead).
Fast forwarding through many hours of welding, I had a ladder frame joining the B-pillars and linking to the rear shock towers and wheelarches:
Along the way I had to remove the backlite (rear window) and excise the rear parcel shelf to get better access to the tops of the shock towers. It was a weirdly anticlimactic point of no return.
By this point I was itching to behead the car, but more had to be done: completing the structural rear window frame, welding it to the tops of the B-pillars. I used bolts in rivet nuts as temporary welding fixtures.
First use of the car as an actual pickup truck - I did all the fab work in a loading bay / rudimentary machine shop at work over weekends, so I had to clear out every Sunday night and park in another office parking structure a mile away. Hence the blue-taped third brake light.