  We extend the Shirafuji model for massless particles with primary spacetime
coordinates and composite four-momenta to a model for massive particles with
spin and electric charge. The primary variables in the model are the spacetime
four-vector, four scalars describing spin and charge degrees of freedom as well
as a pair of Weyl spinors. The geometric description proposed in this paper
provides an intermediate step between the free purely twistorial model in
two-twistor space in which both spacetime and four-momenta vectors are
composite, and the standard particle model, where both spacetime and
four-momenta vectors are elementary. We quantize the model and find explicitly
the first-quantized wavefunctions describing relativistic particles with mass,
spin and electric charge. The spacetime coordinates in the model are not
commutative; this leads to a wavefunction that depends only on one covariant
projection of the spacetime four-vector (covariantized time coordinate)
defining plane wave solutions.
