I consider the factory system a bit lame. You have to pull the lever just the right amount. Too much and things don't move. This may be from wear, given that the truck is 51 years old. I flogged that adjuster for awhile when I had the seat upside down after putting on the new upholstery. Got tired of that and worked the adjusters so that the seat is all the way back on both sides, since we all sit with the seat all the way back, anyway.
Don't touch that knob! ...or dial, as the Wolfman used to say.
LMC sells a cable with a turnbuckle. That system may lend itself well to the appropriate amount of movement with each adjuster.