The long gold prop hub is only for Corvair engines wich will not be using a 5th bearing. The design predates 5th bearings, and was at that time our “standard” hub. With the arrival of 5th bearings, we developed the Short gold hub, which kept the overall length of the engine identical, precluding the need to change the length of existing cowlings.
A machining technique of shortening the long hub was developed by Jim Weseman to allow people who already owned a long hub to use it with a 5th bearing. The need to this has dropped off as most engines today have been retrofitted with a 5th bearing, and almost all new engines are built with a 5th bearing and a Short Gold Hub.
We still offer the Long hub as a catalog part, but I highly encourage all builders to use a 5th bearing.