According to very old special service messages from Ford, you should not use Mercon V or any synthetic or synthetic blend Mercon fluid in that trans.
Some over at www.escape_central.com have reported problems using Mercon V.
This is complicated by the fact that Ford now is pushing the idea that Mercon V can replace Mercon, but they havn't put anything in writing specific to this transmission.
I have seen Mercon V used in this trans with no apparent ill effects, but I would still not take a chance.
By the way, I have never seen a Mercon rated fluid that was not also Dexron III rated and vica versa. Mercon is the Ford spec and Dexron III is a nearly identical General Motors spec. Any blender that meets one of the two has no trouble meeting the other.
