  We discuss how existing astrophysical measurements of various 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 discussed in this workshop (and elsewhere in this
volume), our analysis serves as a proof of concept as new observational
facilities will soon allow significantly more robust tests. Importantly, 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 (and
discussed in the previous contribution).
