Most use railway rails set into concrete,and a selection of hydraulic rams and chains.....I once bought an ex army truck that the grunts had turned into a banana with the winch,bend was just short of busting the transfer case ......anyhoo,I took it to a truck aligner,they removed the fuel tanks ,and had it back straight in a couple of hours work....they had used a lot of heat,but it wasnt a heat treated chassis,so just a repaint...........I turned a $500 write off into a very low mile 4x4 truck I sold for $7000......