  Observations of core-collapse supernovae (CCSNe) reveal a wealth of
information about the dynamics of the supernova ejecta and its composition but
very little direct information about the progenitor. Constraining properties of
the progenitor and the explosion requires coupling the observations with a
theoretical model of the explosion. Here, we begin with the CCSN simulations of
Couch et al 2020 ApJ 890 127, which use a non-parametric treatment of the
neutrino transport while also accounting for turbulence and convection. In this
work we use the SuperNova Explosion Code to evolve the CCSN hydrodynamics to
later times and compute bolometric light curves. Focusing on SNe IIP, we then
(1) directly compare the theoretical STIR explosions to observations and (2)
assess how properties of the progenitor's core can be estimated from optical
photometry in the plateau phase alone. First, the distribution of plateau
luminosities (L$_{50}$) and ejecta velocities achieved by our simulations is
similar to the observed distributions. Second, we fit our models to the light
curves and velocity evolution of some well-observed SNe. Third, we recover
well-known correlations, as well as the difficulty of connecting any one SN
property to zero-age main sequence mass. Finally, we show that there is a
usable, linear correlation between iron core mass and L$_{50}$ such that
optical photometry alone of SNe IIP can give us insights into the cores of
massive stars. Illustrating this by application to a few SNe, we find iron core
masses of 1.3-1.5 solar masses with typical errors of ~0.05 solar masses. Data
are publicly available online (\url{https://doi.org/10.5281/zenodo.6631964}).
