I took a break from driving my 1st gen 4runner for two months and man do I notice the harsh ride that the 2-3" OME lift gave it.
It is a straight axle so theres that, but damn is it harsh. I had the tough dog lift on my fj60 and that rode sooooo nice. Wonder if Tough Dog makes a lift for your truck or maybe even Dobinson. Edit:
just found this, might be worth giving them a call. I hear nothing but good things about their stuff.
31's will fit fine on your 89' pick up. Maybe torque the torsion bars a tad with some new shocks and then refresh your rear leafs and shocks?
The best ride I had on my old 89' 4runner was blazeland longtravel with the Zuk mod in the rear. The Zuk mod was so simple and effective.