I have a Saltzman camera stand, which I believe is identical in the counterbalance situation. My Saltzman stand does not have a crank, but rather a friction knob attached to the rising and falling head, you loosen up this knob and just raise or lower the head (camera mount, or enlarger head). The weight that runs inside the column..you say it is missing? Or is it inside with no chains attached? Photos would help. I don't see how a weight would be "special" except it is shaped to fit inside the center column. You "could" make a new weight out of lead, which melts at reasonably low temperatures (for metal) of about 550 f.
If your enlarger has a crank, it would operate on a toothed portion of the column, I cannot envision any way a crank would do any good on the chains.
Now my Saltzman STAND is on casters, and there is a crank attached to a chain that runs between each foot of the stand and you crank THAT chain to lower feet to the ground to stop the stand from rolling around..but this system has nothing to do with rising and lowering of the head.