Assessing rust on a 1967–1972 C10 before you buy
Where these trucks actually rot, and how to tell a repairable shell from a parts truck in an hour with a light and a magnet.
Inspect the cab first. On 1967–1972 C10s the cab mounts, rocker panels and lower cab corners decide whether a truck is a project or a parts source. Bring a bright light and a small magnet: filler over rusted metal is common on trucks that have already been repainted once.
Check the floor pans from underneath rather than through the carpet, and look closely where the floor meets the rocker — that seam traps moisture and rusts from the inside out. On a fleetside bed the floor is bolted down and usually corroded around the mounting points; a stepside bed hides less, but its wood floor decays.
The frame rails under the cab and above the rear axle deserve the same attention. Surface rust after five decades is normal. Flaking, layered scale that a screwdriver pushes into is not.
Finally, price the repair honestly. Reproduction cab corners, rockers and floor pans exist, which is good news — but a truck needing all of them plus frame work is a restoration, not a weekend fix.