Keep the grille with you while you work, so you can check your progress and don't be afraid to reset things several times to get your angles right. It doesn't hurt to have a heavy duty ratchet strap laying around in case you need to hook onto the ranger and change your angle slightly. I have one spot on the farm where I do this and it is a grove of 10-12 inch white oak trees where I have lots of options on trees so that I can get the right pull angle. The hardest part about that spot is getting the truck squeezed in between the trees.
I have straightened unibodies this way by chaining the car to a tree at the point of bend and hooking a come along to the front bumper pullling the opposite direction.
For the fine tuning, buy a large eyebolt, washer, and nut and thread it into existing holes in the core support. Then hook the come along to that. if you just use the chain hook on the come along the body panels tend to twist as they straighten.
My dad taught me to do body work this way. He said it was common growing up in Kentucky.