One of my upcoming Bonus materials will be tips, tricks, & suggestions for using FFXd20 classes/items/monsters in a standard D&D game. The conversion isn't very involved, as I've hewn quite close to D20 rules; the largest change is the MP system, really. If you change the use of Magic Points into a more Vancian paradigm, then the classes & monsters shouldn't cause many problems at the table. I will have more details in the official entry.