Putting enough torque on that bolt to try to turn a seized-up engine will do one of two things- - - -strip the threads or break the bolt, or unscrew it, depending on which way you're trying to turn it. Neither one will help accomplish anything. I second the suggestion to jack the truck up and pry on the flywheel teeth, BUT- - - -given the terrain you're working on, use big square wood blocks like sections of railroad ties, not jack stands, to support the frame. Unpaved ground is notorious for letting a jack stand sink in and tilt, and dropping a vehicle on yourself isn't a good thing!
Jerry
