It's ironic that yesterday in another thread someone wrote that as long as your truck is level everything is fine with your torsion suspension, and then you post this.
A few years ago an engineering student, Cristina Jopa did a great research paper on steering and front suspensions in Formula A cars. "A" cars are research cars. Do an internet search and read it. A lot of math but she does a good job of explaining.
Also do a search on steering and torsion bar suspension failures that have to do with front end alignment.
If it isn't too late, have your mechanic check your alignment. Does or did putting your front end in alignment result in anything being out of spec? Particularly castor and toe-in? I don't know what the specs for the 150 are, but typically somewhere between 0 and +1 degree with an adjustment limit of around +4 degrees. In your searches, if you do them, you will find failures where alignments are maxed at the 4 degrees to get a front end aligned.
I've seen this failure of yours before but not with your history. Are you the only owner of the truck? Back in the early 80's I resigned from the service to go back to school and while waiting I took a job with an engineering firm that was modeling what's called the moments of inertia under different loading conditions. The reason for the modeling was because of steering and suspension failures that happened mostly because of plowing but there were other conditions also.
Anyway, examining your alignment is the place to start and don't ever buy into everything is OK if the truck sits level. It's just not that simple. It also doesn't mean something is wrong either. The steering and suspension are tied systems and when tracking a failure you have to start somewhere.
If you read Cristina's paper, pay attention to "bump steering." Not to be confused with bump stops of torsion suspensions. For more general information look up the failures in early Chrysler torsion suspensions when used with leaf springs in the rear, and Porsche's research and their use of torsion bars.
The bolt spacing? I was in a hurry last night and I'm just trying to figure that one out. Seems no one has an answer about why the 2 spacing's were used.