Abstract: A flathead adaption system for an engine adapts the engine to look like a 1950's flathead engine. First the existing valve cover is removed from the engine. Thereafter, an adapter member is mounted at a valve cover opening from which the valve cover was removed. A rectangular plate-shaped flathead member is mounted to the top surface of the adapter member covering over the valve cover opening. The flathead member is provided with a plurality of non-energized spark plugs. When one or more of these non-energized spark plugs is removed, the resulting aperture is then used for pouring oil into the engine in place of the oil filling aperture in the valve cover which was removed.