Hey Blueboy, welcome to classicbroncos! Looks like you've been lurking and looking (for a Bronco?) for awhile now.
Glad you're digging through the threads before just jumping in with both feet (or all four wheels as the case may be) and making sure you do the right thing the first time.
I would agree with Mike above, that I have not heard of Duffs (or most others for that matter) coils sagging any sooner than could be expected normally.
Any spring can sag over time of course. But most of the quality ones don't. At least not anytime soon. The leaf packs are more prone to do that sometimes, but even with them most normal use won't see you sagging beyond use anytime soon. "Normal" being the operative word there though!
The variable rate coils are pretty soft initially, so if you run them for awhile, then add a heavier bumper, or even if you do it right away, that extra weight is going to take the soft coils down a notch. And perhaps a little more over time as well.
That's not sag though. Just "settling in" under the additional weight.
Might be what some are calling sag. Which it's not, at least in the way we're thinking of it.
I still tend to disagree (but only mildly) with those that say dual shocks are no longer necessary ever. Those that list the qualifiers (such as the previously mentioned dune hopping, or perhaps good ride quality) are more correct to my thinking. The heavier your rig, sometimes the more justified the duals. Or the more you use it hard, or if you want some tighter cornering characteristics (on the road) and don't want to use an anti-swaybar kit, then duals is another way to get that.
But generally yes, they're correct to say that with modern shocks most Bronco owners no longer need dual shocks to get the best of both worlds. Sometimes you can try singles first, then go the dual route if you think it's not enough.
Or you can have custom valved single shocks (pretty expensive usually) or Rancho 9000 adjustables. But as cool and handy as that adjustability is, I still don't think there are many that think they've got the best of both worlds at any setting. Either too stiff, too soft, too harsh, too mushy. Never "just right" like some other, even less expensive shocks.
They're good. Just not as good.
I like to recommend the Bilstein shocks that the others have said too. Great for many different Bronco setups, and most users (by a wide margin) like them a lot.
A few of us, including me, find the standard valving for a front shock a bit light for a front heavy Bronco (there's that winch and bumper again), and you would do well to consider a heavier valved version if yours will be heavy with accessories. Or even go custom valving?
I actually still like mine, even with the heavy bumper and moderate sized winch. They're just borderline soft.
You going to stay relatively light with yours? No big bumpers, big tires, big engines, hard tops or big gas tanks and such in other words? If so, then yeah, I'm thinking that a single shock per corner like has been said, would be your best bet.
Add a bunch of weight though, or add harder more aggressive use, and that could change.
Other items to consider for your build:
While longer parking brake cables are not a requirement for the street and super mild trails, they are one of the early limiting factors in wheel travel once you get to 3.5" of lift and want to utilize all it's potential.
The modern leaf packs from us (WH), Duff and BC and others are capable of flexing like nobody's business compared to the old ones. Shocks and brake lines and cables soon become the limiting factors in that equation.
Don't even think about running stock length brake hoses though. It's ok to pull up hard against an armored parking brake cable now and then. But a rubber brake hose? Not so much!
Dropped pitman arm and trackbar bracket.
Degreed shims likely needed (so expect that) for your rear lift to correct the pinion/driveshaft angle.
Adjustable draglink to correct the steering wheel position in case the drop brackets don't quite get it re-centered.
Adjustable trackbar to lessen the load on the bushings from the tilt of the mounts after the lift.
Better brakes are a given, if yours are not already updated.
Driveshafts are not usually needed for 3.5" of lift. But they can be, as many here will attest. You have to measure to be sure.
Some of the above are just options, while some are mandatory.
Where do you live and how is the Bronco set up already?
How often are you going to drive it? Summer heat? Bumpy roads?
Sound and heat insulation of some type (don't scrimp here!) will go a long way to keep the family members (insert spouses name here) happy. The kid dropper offer mode will be enhanced too, although they tend to think it's all cool depending on their age and how much work you let them do with you as it's being fixed up.
In that vein, make sure to add any good pictures you get of the kids-and-Broncos to the others we have here. When you have your Kodak moments with the kids and spouses and even the dogs (if applicable) during the build and after, when enjoying the fruits of your labors, we like to share in them too.
Or of the shop labor if you're having one built for you!
Are you going to cut and flare the fenders, or remain uncut? Your choice of tire sizes is very dependent on the other things you do. Sounds like you want to go uncut, based on the stock wheels/hubcaps and small-ish tires comments. That the case?
There are many threads hereabouts showing pics of different lift heights on uncut Broncos. Have you checked them out to make sure you like the taller LUBR (lifted, uncut Bronco) look? Some prefer the 2.5" or 2.5 + 1 height to the 3.5, or 3.5 + 1. While others prefer the taller setup. Definitely worth looking at the differences even 1" makes.
And more important sometimes, that 1" here or there definitely makes a difference to other family members. Kids and adults alike.
Best if everyone is on board!
Good luck. Hard to say what's "best" for everyone sometimes, but you'll get good info from the members here. You'll quickly see that not everyone has the same tastes, but they'll give you accurate info as far as they're concerned. Which is why you often come out thinking you just got 10 different answers to one simple question about "the best" of something.
Just don't expect a full consensus on what is best in any one category. You read the "what's the best carburetor" thread yet?%)
You'll see what I mean...;D
Paul