The flaps are about 3 ft wide (Same depth as ailerons) and start at about 6" from wing root. And no, I don't have a crop duster model. Been lookin' for years for a 188 (Ag Truck or Ag Wagon) but all I can find is Kyosho (spell?) something or other ARF. wish there was a kit somewhere. I'm not good enough for scratch built.
I've got about 6,000 hours in the Cessnas and another 2K or so in Ag Cats and Pawnees.