The Ariel singles that are in the USA are the same as mine which is an All alloy 500 single in a later Swing arm frame I always thought mine was somebody's mongrel and never seen one in the UK but apparently the two that are in the USA are the same 1952 Alloy engine in a later swing arm frame they were bought as Cyclones according to their orders so some confusion ..
The original VHA all alloy engine was fitted to the Ariel plunger frame in 1962 and painted a light blue for the Queens Coronation only 200 made. The engine is entirely different to other Ariel engines.. if that explains the difference.