After spending years and far more money than I ever care to admit building and rebuilding and rebuilding my '89 truck, I can tell you what I would do if I had an oppertunity to do it all over again or build that Runner.
First of all, what you build entirely depends on what you plan on using it for. The general purpose of most rigs on this board are traveling long distances, with improved off road capability, but not necessarily extreme off road capability at the expensive of on road driveability.
With that in mind, I would keep the IFS and limit the tire size to 33s. I'm a firm believer in absolute minimal lift. You don't need 4-6" to clear 33s. 1-3" will do it just fine.
When I did my minimal lift to fit 33s, the ball joint spacer mod wasn't available. I think that's an excellent alternative to cranking up the T-bars for about 1" of lift, which is what I did. Keep the T-bars as stock as possible. You can crank a tiny bit if needed, but stock is better for overall ride. The spacer will give you about 1" of lift or so and that should be plenty to clear 33s. Especially if you run stock rims or at least stock backspacing.
You may need to remove the inner fender skirt and front mud flaps. Triming the rear lower fender lip would help a lot if additional clearance is needed as well as pounding down the rear firewall fender seam.
The front upper and lower bumpstops can be cut down or replaced with low profile units that will help with articulation. Removing the sway bar is a popular mod, but I just wouldn't do it. The minimal extra articulation you would get is not worth the reduction in highway handling.
As for torsion bars...stock work just fine. Larger bars will not get you any additional lift nor will they allow you to crank higher without and drawbacks. Where larger bars have advantages is if you have a heavy bumper or winch, they will help keep you from bottoming out when going over rough roads. I would not ever go larger than 25mm. Sway-a-way makes (or at least used too) a good 25mm set of bars. Stay away from 26mm or larger that some companies sell.
The stock steering on IFS rigs are very good, but now's a good time to go through it if it hasn't been rebuilt. Toyota is offering a recall on the center tie rod. Get it done if you haven't already. Replace the tie rod ends if they need it. The idler arm is common failure point on the steering, although I never had a problem. Not even with my long A-arm set up. At least have it checked out, rebuild or replace if necessary and get an idler arm brace, such as from Downey. The best option is a new super beefy unit from Total Chaos and then you could just forget about it, but they're spendy.
One last thing on the front end....pick up a cheap used half shaft and toss it in the back along with a tool kit. They're the same for either side so you only need one. If you wheel a lot and wheel hard, you'll very likely end up breaking an axle eventually. The most common break point is the CV outer shaft that attaches to the hub. Replacing the whole halfshaft as one unit is the easiest fix.
Moving on to the rear suspension. This one is tough, because it entirely depends on how much weight you plan on carrying. My first choice in springs would be ARB's OME springs with about 2" of lift. This would give you some wiggle room if you end up adding weight. If the OME springs still sag with excess weight, you have two additional options to compensate. My first choice in secondary compensation would be longer than stock shackles. These actually improve articulation and don't harm ride quality while giving you from 1/2 to 1.5" of lift all by themselves. If additional weight compensation is needed, you could install add-a-leafs. I've used both in my truck.
Another cost effective option is to keep the stock rear springs and just go with the combination of add-a-leafs and longer rear shackles. I used this set up for years with great success and the cost was only a fraction that of new springs. The top alone will add enough weight to keep the ride from being too harsh with that set up.
Once you get that done, then it's time to start thinking about gearing and lockers. With 33s, you're choice is 4.88s or 5.29s. I personally like 5.29s for a number of reasons. Better off roadability, better acceleration around town, etc. But they result in higher rpms at any given speed than stock. 4.88s are better for returning your rig to stock rpms at any given speed. 4.88 diffs are usually easier to find and you can find them in wrecking yards on stock Toyotas made from 1992-1995 that came with the V-6 engine, auto trans and 31" tires. Buying stock used diffs is probably the cheapest way to upgrade the gears. Plus you'll end up with a stronger rear V-6 type diff. But for a very heavily loaded rig, I would opt for the 5.29s.
Lockers are where the real expense comes into play. In my opinion, the rear should be locked first, instead of the front. An expedition rig, needs the ability to drive in 4WD in various conditions at speed and that means an open front diff and that means either no locker up front or an expensive on/off type locker, like an ARB electric locker. For the rear, any locker or LSD will work. A lunchbox locker like a Lockrite will work just fine and will be very cost effective.
You'll find with 33s, a locked rear diff and at least 4.88 gears and about 1-2" of lift, you'll be able to follow more built rigs further up the trail than you might imagine.
Since the lift is minimal, so will be clearance. The 4Runners have an issue of the gas tank hanging down lower than the pickups. I would beef up the skidplate on the gas tank. On option is removing the skid tank and welding steel angle iron as extra bracing. If you opt to go with a 1" body lift, which is an option, but one I don't really like, you can lift the gas tank at least 1" and gain some clearance that way.
For the center crossmember, Budbuilt makes a crossmember that increases your ground clearance and covers most of the transfer case with heavy duty steel plate. I would highly recommend this part on a rig with minimal lift that plans to see any rock crawling or serious off roading.
In building my rig from stock, to modified stock IFS, to long A-arm suspension, to solid axle swap, the best set up I ever had for the type of use we often discuss here was when I ran 33s on the stock IFS with minimal lift. And I'm basically describing that build with some additional mods that I would do if I could do it over again.
Don't get me wrong. I loved my SAS truck and it was fun as heck to drive off road, but there were many a time, when I longed for my stock suspension. Pretty much anytime I was on any twisty paved road. SAS trucks can be road worthy, but for long trips and a daily driver, nothing beats stock or modified stock. And while Toyota's IFS may not perform as well as an SAS truck, it works much better where the rig will see 90% of it's use...on the roadway, and works just fine for 90% of the off roading most people do.
Sorry for the long post. Hope that helps some.
