Does take some thought to get what you need/want.
On the one hand, it's hard to beat the isolation properties of stock rubber replacements. But we've found so often over the years that early model EB's had such poor caster readings that adding some is usually considered a good idea. So for that, you go to poly and have to choose your degree.
Normally you would just choose 2 degrees for stock, but with that knowledge of too-little caster, the 4 degree versions make good sense.
How is your pinion angle now? If it's in good shape you will easily handle a 4° offset. If not, then you stick with the minimum.
And now to your question of steering. If you have driven your Bronco prior to this, then you will likely feel the difference in steering effort when you add 4 degrees of positive caster. It may not quite be Arnold Armstrong steering, but you will notice it's a little harder to turn when slow, such as in parking lots. When driving? Probably won't even feel it.
But that also all depends on just how much caster you already had. If you had less than 2 degrees positive, not a big change maybe. But if you already had 3 or 4, then I'd say you'll really feel it at 8 degrees!
How long before you change to power steering? If not long, then 4 degrees is probably a no-brainer.
Lastly, is the Bronco drivable at this point? If so can you put it on an alignment rack and have it checked before you decide? If so, that's the best way. If not, you'll have to punt, like so many have on this subject.
If you can't, do you happen to know what your caster was before you took it all apart?
Maybe at the very least you can set the truck level-ish and then put a digital angle finder on some flat surface of the knuckle. One member here recently used the bottom ball-joint as the point of reference. Might be at least very close to the actual measurement, so worth a try if you want to know what's what before choosing what will be.
Good luck.
Paul
