My Mark V has VERY sloppy steering (I can turn about 1/4 without going anywhere).

The car has sat for most of the last 2 years with an occasional run for about 20 to 30 minutes at a time about every 3 or 4 weeks.

Any suggestions where to start looking?

well first off is the drag link, pitman arm and possabley the steering box itself. Jusr jack her up pull the tires, and have someone slowly turn the wheel and look for whats moving and whats not so to speak. more than likely all the joints are dried out and its now metal on metal and you need all the links arm and rod ends. Good luck, good news it most of these parts fit many large ford cars and trucks into the 90's. Aftermarket should be easy.