Ahhh I get it. You want to keep 'er more street legal. Airbags a waste of time! He must not have any experience with them! WOw. My friends own a very successful truck shop and they do airbags all the time with GREAT results. The local fire department even insisted that they put aigbags on their trucks because they are perfect to maintaining a great ride when you want smooth and then they increase your carrying capacity when activated. Properly installed, you won't even notice any difference. They are super soft and flexible when not inflated. You would love them because you get your nice smooth ride and then you pressurize and adjust them when you carry a load or hook up your trailer.
To keep your rear axle in check you'll need new leaf springs of course. Old springs absolutely cripple Toyotas. The stock springs are the worst and wear out very quickly. I know they issued a recall for the earlier US trucks and changed the spring strength altogether at that point. They sell them weak so they ride better. The stock springs aren't designed to arch much and the hangers don't allow and weren't designed for it either. All that wasn't needed since they didn't design it for more than a few inches of travel anyways. I've seen supercharged Tacomas with bigger tires burn rubber down the street with no problems. They easily put out as more power than the stock 1UZ so you will be safe with upgraded springs with longer decent shocks. Just use arched springs for more wheel travel and don't use spring/axle blocks if possible. This is easily the easiest and cheapest route. I would recommend doing these mods and then adding airbags after you have driven around for a while. Airbags are really great as long as you stick to the main brands like Firestone.
Good quality coilover shocks are very expensive as I think that anything less than the expensive ones is absolutely unacceptable. I've seen so many cheap coilovers break from moderate use. The quality coilovers only break/bend when a race truck takes a huge hit that would crumble a regular street truck.
You can go with upgraded leaf springs, new upgraded spring hangers, poly bushings with new longer travel shocks and be competely happy. This is by far the easiest way and you can change the leafs out and the shocks to make adjustments instead of having to rely on someone to tune coilovers. The whole coilover setup will have to be fabricated and cost MUCH more (tons of labor to have someone built it)... and cost more to have someone set it up properly to your needs. I love cutting and changing things out but in your case that's not really an option it sounds like. The green truck above really doesn't have any more parts added besides what I just mentioned. Well if also has an extended brake line which is simple.
Take a look at Donahoeracing's website
http://www.donahoeracing.com/index.php as they have the best rear Tacoma package on the market. It's worth every penny. This will give you some ideas and something to consider. I've just seen what works and can tell you where you'll get the best bang for your buck. Of course I'm just trying to help. I won't be offended if you try and adapt a whole multi-link system from another vehicle to your truck =] Heck, I was considering using Nissans independent truck rear suspension under my Tacoma!
Here is a pic of the shop trucks and mine on the end behind them. My truck really isn't that small, both of the trucks in front are really really big. Look how high you have to step to get into the blue Ford. There are motorized steps that come down when the door opens but it's a long way up.
The truck has nice soft springs and big airbags for when he towns his fishing boat and other things. When he first showed off the bags to me he dropped the rear of the truck when I was sitting on the tailgate and it actually lowered
down quite a bit. The system flexes a whole lot as I have been in the sand dunes with this truck. It's just a regular set of soft leaf springs and a regular set of adjustable Firestone airbags. I've seen him do this on a lot of work trucks and play trucks with 100% happy customers and many referrals from them. Just paint everything black underneath a Toyota and all is legal. Fun stuff!
Here is me holding a HUGE coil shock which was designed for a full size Ford F250 4-door. This is the biggest coilover shock you can buy in a street legal (United States) suspension kit. It was very heavy and I'm gritting my teeth because I couldn't hold it up for much longer.
It takes a few times to custom tune a coil over shock for someones expectations. The coils need to be the correct weight before you can tune the dampening which is done by taking the shock apart. The only way to speed up the adjustments is to use a bypass shock next to a shock that accommodates the coil spring. This is the only way to externally adjust the shock dampening without taking apart the whole single shock to make the internal adjustments. This is a must for racers who need to adjust for different conditions and VERY expensive. Lots of time and experience needed either way with coils. If someone has done a coilover on a Hilux with good results I would like to see it. I have no doubt it can be done but I just can't recall seeing one that would be anywhere suitable for street.
