If we were talking caster in another thread, you should add this info to that discussion as well. At least I think that would be a good thing to do.
Reason is that a +6 reading is HUGE! No normal EB front axle is going to achieve anything near that (even a '76 or '77) without cutting and turning, if it's lifted. Is your Bronco stock height? Did you add 7° C-bushings?
Wandering can be trackbar moving slightly, older tires, too-wide a wheel for the tire, tread wear, toe-in not adjusted to the correct amount, skewed front-to-rear axle alignment, etc. And yes, it can be just an old short-wheelbase utility vehicle's way of driving. It can also be quicker steering and smaller steering wheels, or slower steering and bigger steering wheels. Which one depends on what you're used to.
When does it wander, and how much?
paul