Fortunately, the frame is in a lot better condition than the body. Here I am, doing a little frame surgery prior to boxing the front:
You can use a 6"-wide plate in 1 piece to do the box in the front:
The box is important for rigidity when you put in the IRS. Just be ready to do some long trims. I use the 3" cutting wheel probably a lot more than most folks.
I sure would like to have a plasma cutter, but my torch had to do the job for the IRS C-notch:
Came out pretty nice after adding a little finesse: