I got curious about how much force the chain cutter in the hardware store needed to cut chains and it's easy to figure the same thing with this project.
With a 3' long handle and a person pushing down on the end with 100 lbs force it's 300 ft-lbs of energy.
If 18,000 lbs x X feet has to equal 300 then X = 0.017' or 0.2".
Pulling down the handle using stiff springs from HD will tell you how much force you are using by how much the spring is stretched. Storm door snubber springs take about 40 lbs per inch and you can parallel springs to get more force.
When do we start?