Which he would need to do to add ABS anyway, right ? It only came on the full float trucks, so they are the ones with the sensor mounts. Off the top of my head you would need a full float rear axle with sensors, front knuckles with sensors, birfs with tone rings, the actual pump / valve unit, the ABS computer, new brake hard lines, the ABS master cylinder, the inertia sensor under the center console, and newer wiring harnesses if yours doesn't already have the circuits. All to install a 30 year old design first gen ABS system that wasn't great to begin with (well, it might have been relatively great in 94), and really goes to crap if you upsize wheels / tires. I think Mr. Spock there is one the right track. Start with a full float disk brake rear axle. If you can live without a factory locker axle, they aren't too expensive and will be a decent upgrade to braking performance. If it isn't enough for you, it will at least be the first step in retrofitting ABS.
I really hate to be the guy that says this, but... If you really want ABS in an 80, unless your current truck was free, or you have a free wrecked donor with parts and plenty of time, you would be better off selling your non-ABS vehicle and buying an ABS rig.
Good luck either way !
Jason