The spec's actually call for type "F" ATF but with all the changes in the formulas I doubt it really matters.
I've only tried the synthetic once in my 250C and the results weren't encouraging. Not to say it wouldn't work for you since it appears other members have had good success using it.
I would stay away from the "IV" but ya gotta do what ya gotta do sometimes.
The following is from a "TechTalk" article.
Ford Type F—an old ATF first introduced in 1967 and used in all Ford products prior to 1977, and in some until 1980; also used in various import vehicles of the period, including Mercury Capri, Jaguar, Mazda, Saab, Toyota, and Volvo. Type F is not compatible with any other ATF. Specifically, it is not compatible with Mercon ATFs.
Ford Type H—developed for the C5 Ford automatic transmission introduced in 1981, it has been superseded by Mercon. Type H is not compatible with Type F and should not be used in a transmission requiring Type F.
Ford Type CJ—originally designed for the Ford C6 automatic transmission, it also has been superseded by Mercon and also can be replaced with Mercon V, but should never be used in a transmission requiring Type F. Dexron II is an approved alternative to Type CJ.
Mercon—introduced in 1987 and similar to Dexron II. Ford ceased licensing Mercon in 2007 and now recommends Mercon V for all transmissions that previously used Mercon. Mercon is a suitable replacement for Type H and Type CJ fluid, but not for Type F.
Mercon V—the most common Ford ATF in late model Fords, it is very much like Dexron III. Should not be used in a transmission requiring Ford Type F.
Mercon LV—the latest Ford ATF, it is factory fill in 2008 and later Fords. The LV stands for "low viscosity." It is a fully synthetic ATF. It is not compatible with earlier Mercon fluids, so it should neither be mixed with Mercon or Mercon V used to replace those fluids. It is not compatible with any other fluid, either.
Mercon SP—a version of Mercon V with an enhanced additive package.
Mercon CVT—Ford ATF specifically developed it for models with continuously variable transmissions.
As always, YMMV.