They'll bolt on, but like you said, you'll need smaller wheels. A good set of F-1 fenders, unless you go with fiberglass, are getting next to impossible to find. The F-2 to F-6, while are also getting rarer, are a lot easier to find than the F-1s because they were used on many more trucks, many being farm trucks that were only used during the warm, relatively dry months for planting and harvesting and put away during the winter months. Also, the larger trucks once they stopped working were put out back behind buildings while the smaller trucks were driven until they fell apart.