Just a guess on my part, having seen a few similar looking winches. Probably rated for around 4 or 5 tons. Input shaft is probably a worm gear with a sprocket for a chain drive. Chain drive probably pulled from a pto shaft on truck transmission. Might be just out of sight on right hand side of the picture. Gear ratio is probably pretty slow., but can be changed by replacing drive sprocket. Winch might disengage to free wheel the cable off. looks like there is some sort of brake above the cable drum. With a little fabrication might make a good logging winch for a 3pt setup. If cable has to spool off as well as spool on, I probably wouldnt fool with it. I would inspect the input shaft for play before buying. Bearings can go out and get in worm gear. Last one I rebuilt, back in the 1970's, I was able to buy off the shelf bearings.