I'm not sure the earlier model smoke units work the same, but if they do, the one screw is near the top of the assembly where the top half of the smoke unit (not the piston and lever assembly) attaches to the frame.
The piston and lever assembly fits up into the bottom cup of the top smoke unit. The levers on the sides at the bottom are driven by the main side rod assembly and make the piston go up and down in the cup, thereby "pumping" the smoke out. My recollection is that the levers sit in a groove and nothing on that end is physically attached anywhere. With the piston inside the cup and the levers in a groove and being rotated by the rods, it stays in place. The spring provides the resistance. I believe I purchased a new assembly because the old one was bent and corroded or maybe missing entirely.
If everything is not working properly, the levers can get stuck but the whole piston and lever assembly should basically fall out of the cup once you remove the shell and side rods. It may take some careful working of the parts back and forth to get everything loose, if it is jammed.
The attached pics and video may make it clearer.
