A rear sway bar is another effective option, may be a lot easier to install than a front bar, depending on your front and rear end setups. I put on an Addco rear bar for a while last summer on my '85 and it worked fine. Its off now until I get the rear axle and other stuff worked out, but it made a big difference in handling and will be going on after the rear end work is done.

I also found that issues like minor bump steer are related to overall steering geometry. When I had this problem, I also had problems with wearing front end components like spring bushings and ultimately had problems with death wobble. Fixing the caster angle (I had too little) made the steering a lot more solid and now if I hit bumps with the front end, it stays put.