My track is lowered on 22's. w/ 35 series tire and have minimal rub in very sharp turns. They are 9.5" wide and they have a 1" spacer on them.
My mustang is bagged on 20's and its just my own opinion that unless your going for the show look and not a daily driver then I wouldnt do bags. Just know the problems you can run into w/ bags, especially in the cold weather. Anyway thats my 2cents. Whatever you decide to do please post pics when you get it done.
The usual lowering blocks and Torsion Bar adjustment will only get you about 2". If you want to go lower, you will need bags, but I don't know of anyone who makes a kit specificly for the Sport Trac.
My guess is you would have to buy something for the Ranger or the older Explorer and be prepared to make some modification. If you have the tools and a good knowledge of metal fabrication, etc. it should be a piece of cake.
I've got 22"s with a 2" drop all the way around. They rub a little bit in the hard turns as mentioned above. I also had to trim quite a bit of the plastic liner in the fender wells.