I met with the Thordon bushings guys at Fish Expo. They normally do plastic tugboat rudder shaft and prop bushings. Off the shelf mass produced products are a fine way to keep costs down. They told me that they sell bushings up to 8 feet in diameter. In their experience a polymer on polymer bushing situation is to be avoided. This is however the definition of a Tides spherical bearing.  They look ideal for unstayed rotating mast bearings.  I have been specifying them for rudder bearings on my boats for years now.

http://www.thordonbearings.com/