If there is no way to adjust the FOV beyond what the game offers in its options menu, please first use the G3D FOV enhancement in the vorpX options as far as it looks OK, then use ImageZoom to account for the rest.
4:3 resolutions usually are best for this workaround to minimize black bars. There are exceptions from this rule though, so it might make sense to try both a 4:3 and a widescreen res to check which has less wide bars after adjusting ImageZoom.