  We extract cluster structures and establish spectral coordinates from rank 3
WKB spectral networks $\mathcal W(\varphi,\vartheta)$ when zeros of
$\varphi(z)$ are almost on a line in the complex plane. Then, we provide
solutions to the Riemann-Hilbert problems (cf. arXiv:1611.03697) defined by
these WKB spectral networks, using the spectral coordinates. As an application,
we embed spaces of framed polynomial cubic differentials, associated with these
WKB spectral networks, into spaces of stability conditions, adopting the
approach of arXiv:1302.7030.
