The vertical lift links from the rockshaft are supplied with a cast iron shaft collar and a large square headed set screw. There are three positions for the set screw about 2" apart. This allows for no float or as much as 6". Perhaps one can remove the collar and get even more.
There are also pins with D-rings on the fast hitch sockets. They can be removed, stored in another hole on the receiver, and this permits the Fast Hitch receivers to rotate as much as 30 degrees or more.
So, yes, there is float capability on the later Fast Hitch. I am guessing all Fast Hitches after 1955 can float in this manner. The previous Fast Hitches can float by removing one pin on the vertical lift link.