One of my favorite kits, I often rob this kit for other builds, the wire wheels are great for rat rods as well as the detailed v8.
The rust on this one was achieved with an airbrush, I mixed up some “flattening” agent with black and orange basecoat paint. After spraying that on the area’s desired, I then mixed up some real rust with water and gently apply that over those spots using a brush. When the rusty finish dried, I then used a dry brush to knock of any loose rust dust.