Single-photon emission computed tomography (SPECT) performed with a pinhole collimator often suffers from parallax error due to depth-of-interaction uncertainty. One possible way to reduce the parallax error for a new generation of SPECT pinhole cameras would be to incorporate fiber optics to control the spread of light and improve 3D position estimation. In this work, we have developed a Monte Carlo simulation for an SiPMbased modular gamma camera that incorporates a fiber optic-plate as a light guide. We have created a custom photon transport code written in Swift and we perform the computationally taxing components on a GPU using Metal. This code includes refraction according to Snell's law as well as reflection according to Fresnel's laws at material boundaries. The plate is modeled as a hexagonally-packed array of individual fibers. We also include the scintillation statistics of NaI(Tl) and the detection efficiency of the silicon photomultipliers. We use the simulation code to create mean-detector-response functions (MDRFs) from which Fisher information on event positioning can be assessed. We compare planar detectors with different light guides to determine the effects of the fiber optics. We model three geometries; one that only uses a monolithic light guide, one that only has a fiber-optic plate, and one that has a monolithic light guide and a fiber-optic plate in combination. The spatial resolutions are compared by using Fisher Information Matrices to calculate the Craḿer-Rao Lower Bounds on position estimate variances.