Clayton 7.1 puzzle

[dwallenb]

I am working on a Clayton 7.1 wood furnace in the basement of a recently purchased house. It was improperly used in the past. The 24v Erie motorized air damper actuator on the front will have to be replaced. Currently there is no thermostat at all, simply a wall switch at the head of the stairs to turn the blower (three stage) on, which is set to high with a Clayton three speed rotary switch. There is no fan/temp limit switch on the unit, nor any punch-out places on the rear for one (there is a panel with the punch-out for the optional water coil, but it has never been installed.) What is curious and unknown is an additional panel which is not mentioned in the manual that I found. At the lower left, adjacent to the blower, is a panel with two house rated wires into the top that are adjacent to what appears to be four flat push-in connectors. Below those are four holes, and the bottom three appear to have a flathead adjustable rheostat with a scale around them, showing 100 degrees at the 11:00 position, 125 degrees at the 3:00 position, and 150 degrees at the 7:00 position. My best guess is this is tied into the three speed blower, hence the absence of the limit switch. The value set on the scale determines when the fan comes on. As the temp increases, the additional values (whatever they are set to) are added to the first and then second set points, i.e. if the first is set to 100, the first blower stage comes on at 100, the if the second is set to 125, the second stage will activate at 225, and forth, up to 450. I have attached an image of this panel. Some experienced furnace techs (40-50 years) are also puzzled, but one did offer this possibility. Any comments, experience or suggestions on what I am dealing with? I can restore it in accordance with the manual, but don't want to duplicate or install counterproductive components.