i would use mercon 111,spoke with a ford trans teck,he recommended murcon. used it in aa older mercedies with slipping shifts. cured it.
frend with a twin disc marine gear was slipping( mg507 )we put mercon in 3 years ago just now slipping again.  shifts to harsh just back off the throttle pres

After looking for Information online it looks like Dexron 111/Mercon is the latest recommended replacement for Type A. Really difficult to get straight Information to a simple Question. So many variations.on  ATF now.

  

This was posted by a forum member 7 years ago. Prolly still applies. If in doubt you could ask a transmission shop what they recommend. Find one that's been around a few decades.

The older Fordomatics, (pre 1958) called for Type A automatic transmission fluid. (There is also an aluminum case Fordomatic 2spd that came out in 1959. I don't remember what trans fluid was recommended) Type A has been replaced by several different Dexrons and what is now Dexron III.Type F fluid came out for use in the new cruise-o-matic transmissions in about 1958. Type F was also used in the FMX and most pre '77 Ford transmissions and in some other Ford transmissions til 1981.
Most oil manufactures list pre 77 Ford's to use Type F as they seem to believe there are no Fords still running that are older than 1958.Type F has a higher viscosity than Dexron III and a higher heat tolerance. Dexron has more lubricity than Type F which makes a softer shift compared to the Type F which is more firm or harsh.The key thing is;  use what you transmission rebuilder advises as he may has installed the newer bands and clutches that use a material that requires a Dexron III fluid. Also he is the guy who has to provide warranty.Do not use the newer fluids such as Mercon V which has a very different formula used for the lock up converters.There is newer Type FA on the market which is supposed to be a replacement for Type F and superior to the original Type F. I am not up to speed on it.here is some interesting reading on the Type f vs Type A and Dexron fluidshttp://www.pennzoil.ca/documen...
http://www.hwpetro.com/_fileCa...
http://www.mobil.com/USA-Engli...
http://www.redlineoil.com/prod...
http://ezinearticles.com/?Use-...marv

This was a huge debate for me when I got my Fairlane and was going to fill the transmission for the first time. I WANT to say Dexron 3? Anyone wanna correct me?

The original Fluid was Type "A". What is the recommended replacement Fluid. I have Type "F" in mine now but I am going to replace the Trans. with another 56 Fordomatic which is supposedly rebuilt and never installed. "F" Type, Mercon II, Dextron?  Which is correct?