In application to benzene-Ar we test a procedure that makes use of conveniently calculated J=0 intermolecular eigenstates to compute molecular constants and transition intensities without requiring explicit diagonalization of the full rotational/intermolecular vibrational Hamiltonian of the species. The approach relies on the ability to calculate the orientation of an Eckart body-fixed frame for each point on a grid over which a J=0 state is represented. That ability allows one to compute vibrational matrix elements of operators referred to the Eckart axes while working with J=0 eigenstates obtained in an entirely different body-fixed frame. Generally excellent agreement is found between the Eckart results and those obtained by others via diagonalization of the full rotational/intermolecular vibrational Hamiltonian. Finally, a general prescription for the construction of an efficient rovibrational basis from J=0 solutions in a convenient body-fixed frame is presented.