But it sounds like you have a model of the full size boat built in 1914. These yachts are still sailing so one of the owners might be able to help, details can be Googled.
Further to my previous post, I understand that the Metcalf Moonbeam is derived from an old model 'pond yacht' which may have been inspired in turn by the original full size vessel. It is very unlikely that you will find any scale model making plans available for Moonbeam IV and the best route would be to follow the Google links as suggested above.