  We point out that existing astrophysical measurements of combinations of the
fine-structure constant $\alpha$, the proton-to-electron mass ratio $\mu$ and
the proton gyromagnetic ratio $g_p$ towards the radio source PKS1413+135 can be
used to individually constrain each of these fundamental couplings. While the
accuracy of the available measurements is not yet sufficient to test the
spatial dipole scenario, our analysis serves as a proof of concept as new
observational facilities will soon allow significantly more robust tests.
Moreover, these measurements can also be used to obtain constraints on certain
classes of unification scenarios, and we compare the constraints obtained for
PKS1413+135 with those previously obtained from local atomic clock
measurements.
