Whats the difference between a 980G and 980G series 2 torque converter?
No difference except for certain machine arrangements such as logging or waste handling where they add or remove a Sprague clutch allowing a freewheel stator.
the G2 has a "free wheel stator torque converter", what is the difference between this and a "fixed stator torque converter?"
The stator is the center member in the converter, a fixed stater is splined to the main support, the "free wheel stator has a one way bearing that rides on the main support. Under load it locks the one way bearing, when coasting or idling it is free to roll. The theory was that a fixed stator would generate heat because the oil had to go around it where the free wheel stator would let the oil move easier. Clark stopped using the free wheel stator because it caused too much trouble and if someone rebuilt the converter and put the bearing in backwards you wouldn't have any power just a fluid drive.
so does the free wheel converter act as a "lock up" type?
No, a lock-up converter is something else. The free wheel stator just reduces heat and fuel consumption, but is otherwise just a torque converter. A lockup converter adds a clutch that can lock the driving and driven ends together like in a direct drive machine, to get more power to the wheels by eliminating the slip in the torque converter. Usually the clutch in a locking converter is controlled by a computer.
:exactly