here's what i did (not for lift, but for a heavier diesel engine): got some downey HD torsion bars. yes, downey is r.i.p. but i suspect they are about the same as the bars off a '86-'89 1 ton taco, like the taco cube vans u-haul used to run. other shops may have something similar.
the problem is that the diameter and number of slpines on the front end of the torsion bar changed after '84. so, i called
California Mini Truck and got a pair of torque arms (the bit on the lower control arm that the torsion bar "plugs" into) and a pair of the main pivot bolts that go through the arm (the rear of the pivot bolt is splined to fit in the front-side of the torque arm).
the '85 torque arm fits on the lower control arm pretty nicely, only it is a bit longer. only need to drill a couple of holes on either side of the control arm to accomodate this. at the same time, i replaced all the bushings/seals etc. on the lower control arm pivot, since it was all apart anyway. pretty simple mod for a 1st gen 2WD pickup. this way, you can "crank in" tons of lift without the wimpy stock torsion bars crapping out.
needless to say, you will require some other mods (and a proper alignment) to accomodate such a huge lift, but this will take care of the torsion bars at least. all in all it cost less than $400.