Ray-tracing based methods for 3-D modeling of magnetic field and particle motion in spiral scaling FFAG accelerators have been developed. This allow efficient simulation of 6-D particle motion in presence of strong field non-linearities and possible field overlapping in configurations of neighboring magnets, thus yielding a performing tool for spiral FFAG lattice design and optimizations, and for 6-D tracking studies. It is applied for illustration to a principle design of, and simulation of an acceleration cycle in, a 200 MeV range (radiotherapy class) proton FFAG.