[AZKen]

It does look like the sway bar on his donor 1975 would fit. An anti sway bar is just a bent torsion bar. It's worth a try and should be easy to install. Get a donor sway bar that is 1" diameter or bigger. I don't know the specific engineering explanation coil vs bar in regards to what is actually happening. The coil spring will compress/extend and lean when cornering. The torsion will twist. The coil is a tall feature compared to the torsion bar down low. Have you tried to adjust your bars full one way and then another to see what that does to the sway? Not hard to test that if they are adjustable.
Question: What exactly is your truck doing around corners? Will it stoop down? spin out? heavy body lean? sway all over the road? It does not make since that you have to go that slow? What kind of corners ? and how fast do you want to go around a tight corner? Barry says they are leaners. Maybe torsion bars loose their temper or get fatigued after 50+ years.