This series of engines are usually to be found on ride-on lawnmowers and garden tractors but can also be used on other high spec applications.
They have the two cylinders arranged in a "V" orientation at approx 45 degrees from each other. The spark plugs are fitted fairly deep to the side of each rocker cover.
The air filter is usually a large diameter, round cartridge inside a square metal cannister or a flat rectangular cartridge inside a plastic retainer. Both can be found at the front of the engine. The 54 and 61 series engines may have an alternative multi-stage cyclonic air filter with smaller diameter cylindrical air filters in a tubular housing.
"Vanguard Twin" is usually written fairly prominently on a sticker.
The Model, Type and Code numbers are stamped either into one of the rocker cover sides or on a small alluminium plate rivited to the top or side of the main engine cowling. The Model begins with either 29, 30, 35, 38, 54 or 61 The 54 and 61 models are generally referred to as "big block"