  We study theoretically magnetically induced Feshbach resonances and
near-threshold bound states in isotopic NaK pairs. Our calculations accurately
reproduce Feshbach spectroscopy data on Na$^{40}$K and explain the origin of
the observed multiplets in the p-wave [Phys. Rev. A 85, 051602(R) (2012)]. We
apply the model to predict scattering and bound state threshold properties of
the boson-boson Na$^{39}$K and Na$^{41}$K systems. We find that the Na$^{39}$K
isotopic pair presents broad magnetic Feshbach resonances and favorable
ground-state features for producing non-reactive polar molecules by two-photon
association. Broad s-wave resonances are also predicted for Na$^{41}$K
collisions.
