Angular distributions of photoelectrons emitted from fixed-in-space molecules have become an exciting new tool for studying electronic structure and dynamics. We here use multiple scattering photoelectron diffraction (MSPD) theory to calculate the final-state wavefunction of the electron leaving the molecule and then subsequently its angular distribution. The effects of non-spherical scattering potentials are included in our formalism through non-diagonal scattering matrices, which fit directly into a new approach for multiple scattering theory originally based on spherical potentials. When the kinetic energy of the photoelectron is low (E < 50-100 eV), we find that its scattering cannot be adequately represented by spherically-symmetric potentials. In addition, we have considered the effect of the final-state hole on the wavefunction, and found this to be important as well. Different polarizations of the light are also included. As an example, we calculate the angular distribution of photoelectrons emitted from the K shells of C and O in oriented gas-phase CO molecules, as recently measured by several groups. We show that intramolecular scattering and interference are responsible for the experimentally measured patterns. Particularly important are the energies for which shape resonances appear in the continuum, with the angular distributions showing radical changes over such resonances. We find good agreement between our theoretical results and recent experimental measurements. This MSPD approach thus represents a more accurate and versatile method for dealing with such angular distributions as compared to prior calculations of such effects.