When I was building my '53 it took a lot of metal replacement. It had been a farm truck in the mid west (rust belt) so it was pretty well rusted out. I had to replace the firewall, all the floors, both lower "A" pillars, both rear cab corners, and a 2'x3' section of the rear cab wall behind the gas tank. The only commercial body panels I used were the cab corners and lower "A" pillars. Everything else I fabricated out of 14 and 16 gauge steel sheet.
Cab after paint
"If you didn't build it with your own hands, then its not really yours." - Tim Allen