My suggestions, and I have done this, Put the Bronco on jackstands on the frame. Take the front springs out and put the tires and shocks back on. Now take a floor jack and run the suspension up. At some point you will run into a limitation. Tires into the body, shocks bottom out, axle into the oil pan, driveshaft into the exhaust, etc.
Now measure the gap. You want a bumpstop taller than the gap, they do have some squish to them. Solid poly is generally the least squish (10% maybe?). The new foam rubber cellular factory stuff has a lot more squish factor (maybe 75%?). No solid numbers here, lots of SWAG as for how much it will squish.
This gets into every Bronco is different. What works on one may work on yours, or be completely wrong. You have to figure what works on yours.