The Southern Wide-field Gamma-ray Observatory (SWGO) is a proposed facility for ground-based gamma-ray astronomy. It will consist of an array of water Cherenkov detectors to detect astrophysical gamma-rays mainly in the range of hundreds of GeV up to the PeV scale. To be constructed in South America, it will feature an approximately two-steradian field of view and a duty cycle close to 100%, which will complement the current generation of instruments by extending survey coverage to the Southern Hemisphere. As part of the development of the SWGO standard reconstruction framework, we employ a Monte Carlo template-based method to estimate the properties of the primary gamma-ray (such as core position and energy). In this method, an observed lateral amplitude distribution of a gamma-ray-induced air shower is fitted to the expected probability distribution stored in the templates. We validate this approach by estimating the energy performance for one of the currently investigated test array and detector unit configurations for SWGO.