got a c-channel bumper. what ya think?...
http://www.rivercityrockcrawlers.com/BBSups//WINCHPLATE.jpg

heres anutha...i added the plates behind the bumper instead to make it stronger when pulling...but more of a PITA to make. also some stiffiner bars.
http://www.rivercityrockcrawlers.com/BBSups//WINCHPLATE2.jpg

Well, Depends on how you mount it to the rails...assuming the channel is 1/4 inch and the frame horn brackets are 3/16's it should be ok....my arb bullbar isn't that stout but is square with 3/16'' plate....should be good to go....

Not sure what your plans are but I would mount it above the bumper with the fairlead not forward of the bumper. maybe a 1/4" plate welded to the back side of the bumper, taller and wide enough to configure the mount. The reason to raise the winch is so it isn;t the first thing to hot an obstacle. Also loose the snap rings and pins on the 2 outside rollers, pick up some 6" long 5"8 bolts and nuts. Tighten them down, it keeps the cable from getting pinched in between the mount and roller. No the roller won't roll when this is done, but it beats the alternative, assuming you plan to wheel that rig!