I know the older C-4's use Type F, but at some point in the late 70's Ford started using Dex II.  The 1980 Owner's Manual recommends Dex II.  I am told Type F would provide crisper shifts.  I think Dex II is now Dex 6 and supposedly backward compatible.  I have both Type F and Dex-Merc in stock.  I think Dex-Merc is closest to what the owner's manual suggests.  See attached. 

What are you all using in your C-4's, specifically if you have a 1980 version?  What is the scuttlebutt on pros and cons of both fluids?  I have no history on this tranny, in fact I don't know if it has been rebuilt at some point in the past, or if it even works.   

What would you do if it was yours?  Last year I drained the old fluid, cleaned the pan, and installed a new filter.  By next year I plan to run and hopefully drive it so I want to be prepared with and use the correct fluid. 

Thank you for that answer.  I will use up the Dex/Merc I have in stock.  I think the only other think I have that uses it is the transfer case in my '03 Ranger.