Ahem, well I am thinking of two methods right now, one is make a doohicky so that I can put my torque wrench on the handle of my 8 ton hydraulic jack and use that to measure the force to raise each end of the box. The other is to cut notches in my crowbar to make a 100:1 lever to use with bathroom scales.

Someone showed me how to make a hydraulic load cell but that involves buying a hydraulic pressure cylinder, there there is the option of putting a pressure gauge on my jack but I do not think mine has the required fitting.
Yes there is quite a bit of Lego but not much weight compared to my garage treasures, motors, steppers, selsyns, gears and cogs, funny shaped bits of metal, metal cabinets, 30 years collection of tools, lathe, shaper (very small) bandsaws, cold cut saw, sundry nuts and bolts, transformers of every shape and size, motor cycles, etc etc.