It's correct that the more level you can keep the trackbar the better, but there's only so much correction you can create and even from the factory they were rarely perfectly level. But even more important in the parallel department is that the draglink and trackbar remain as parallel to each other as possible.
This means that with either drop, you should use the other. If a pitman, then use the trackbar drop bracket, and vice versa.

For the most part, all '66 to '79 Radius arms are the same, but with minor variations on the theme.
They''re all the same length and girth, with the same rear stud for the frame mounts.
The caps can vary depending on whether there were factory dual shock mounts, or on some models the standard front shock mount (one in front, one in back of the spring on some models).
The '66-'77 Bronco threaded holes for the coil cups are smaller than the full-size holes. I don't know if this is consistent for all years, but at least for the later seventies full-size trucks and Broncos, the bolts holding the spring cups to the radius arms are larger.

But any of them can be used on any truck. The bushings are identical from '66 to '79 in all positions except for '76 and '77 Bronco upper trackbar bushings, and possibly the same for the pickups those two years with their different steering linkage.

You use what you have to use. Usually C-bushings are my first choice, simply because the drop brackets hang down and don't look as cool.
On earlier vehicles that are ridden hard, they also impart more potential twisting leverage into the frame. Don't remember seeing many that were damaged, but they imparted a bit of a looser feel on the road.

I like to measure caster before installing al ift when possible. This lets you know how much correction you will need. If your cater numbers are close to expected right from the factory, then the minimal C-bushing is all you need to keep it there. If it's way low, like some early trucks were because manual steering was still a thing back then, some trucks might need both just to get them close. But the better method for gaining caster is the old cut-n-turn where you cut the weld away holding the steering yokes (aka "inner-C's") to the axle tubes, rotate them back to the desired caster reading, use 2 degree poly bushings instead of the larger ones, and you're done. It's more work, and usually more cost if you're not doing it yourself, but it's the better way. And the ONLY way you can correct caster AND pinion angle on one of our front ends.

Generally speaking, the stock bar works well with a drop bracket when used with moderate lifts (up to 4") but it's still nice in case there is some fine-tuning to get the axle centered. It's not required to do both, and you an do just the drop first and the bar later if you feel it's needed.

That's incorrect information. It's not the C-bushings that cause the springs to bow, it's the lift itself.
Think about how the springs are mounted and look at the C-bushings location. The bushings can't have any effect at all on the angle of the spring because they're only there to twist the axle back for more caster. But the mounting surface of the radius arm, where the springs are clamped, is tilted more and more as the springs get taller. So the springs are their own worst enemy for bow. An off-center axle can add to the bow just by tweaking them a bit (might make one spring more bowed than the other) so that's another reason for making sure the axle is centered in the frame.

The dropped radius arm brackets main benefit is that it levels out the spring perches and straightens the springs.
The C-bushings main down side, and the reason they only go up to 7 degrees of correction, is that the pinion angle goes down as the caster goes up and the axle tilts back. Luckily, especially with the high-pinion axle this effect is not as dire as on a low pinion front end. But it's still "a thing" to be aware of.

Paul

 

Paul,

Man thank you for all the great info! Gives me a much better understanding.

 

Yes great info. I prefere radius arm drop brackets to keep things to original factory alignment. ( Both ends of the arm drop the same). Been through this three or four times and doing it again on my current setup.

 

So I'm leaning towards either extending my factory arms or buying extended/long travel radius arms. Thoughts on buying new or extending factory arms?

And why does every long arm kit seem to be designed for the Broncos?

 

If you're really good at welding there is probably nothing inherently wrong with welding the extensions on the arms. Many have done it with good luck, but I always felt they were a potential weak point anyway.

My personal reason for preferring the aftermarket arm over the stock one, and a reason all on it's own to go with a longer aftermarket arm, is the "kink" in some of them for more tire clearance.
This one feature has been the main selling point for me ever since the first ones came out that way. One of the coolest things Broncos have is their small turning radius. Larger tires and different offset wheels change all that most of the time, but with the double-bent arms, you get at least some of it back.

Paul