I have an old West Bend engine, I believe it's a 580 or a 700, I can't find any markings that would tell me which it is, It is missing its fan shroud but is otherwise working, the only number I could find was #2703038 on the cast aluminium base pan where the fan shroud would go, I don't think this number though will identify the engine for me, where should I expect to find the number that will identify the engine?