Rock the truck with the transmission in high gear. Any other, and you'll be losing torque by the trans trying to speed up the movement. You'll get a lot more inertia by using the weight of the truck and rolling the rear wheel, rather than trying to turn the output shaft with a bar, etc.
I've got my own little gimmick to keep an engine from freezing up when I'm storing just the engine, not the whole vehicle. Drain as much oil as possible by pulling the oil pan plug, then reinstall it and store the engine upside down. The remaining oil in the crankcase will puddle around the pistons and rings, and will keep the piston rings from rusting to the cylinders. One of my former students used to put engines in long-term storage by dismantling them, putting the parts in a 55 gallon drum with a clamp-ring top, and filling the drum with heating oil. Works for decades!
Jerry
