I expect they are worth less than 1/2 through 1 ton stuff in the same shape, folks don't seem as interested in the big stuff. I know I've picked up probably more than I'll ever need of great rust free and even NOS big bolt sheet metal for not a lot of money.
About all you can do is offer it for sale at a price you're comfortable with and see what happens, then adjust the price accordingly if necessary.
Grigg