I'm pretty sure you can buy full floor pans and trunk floors for early B's now. As long as the bottom of the cowl isn't rotted out, you should be in good shape. The factory never put drain holes in the sides of the cowls on those cars, and water would just pond up in there. I got extremely lucky on the 64 Belvedere wagon I used to have, and it wasn't rusty. I drilled drain holes in the side of the upper cow before it got painted. Glad you found such a great car!