Mine is not a winch bar but was made to keep dairy animals (including stropey bulls that pushed my standard tube bars into the bonnet) and improve the front entry angles for our runoff and fairly easy to make.
I didnt make a photo diary but found a couple of sketches. This photo is the front mount made of 6mm plate.
A pattern was made off the original mounts with a piece of cardboard so it could be shaped into a template and it looked something like the one in the sketch
Then with the original bumper gone I bolted the steel plates on and made the bumper to fit from there. The main beam is a bit of 4x2 channel (only because it is what I had available) but I dont see why you cant use box or whatever. The main beam has a 10degree bend where the mount plates meet - I cut a notch out of the back and folded it welding the fold and the mount plate into it and the cut a notch out and folded again to wrap around the front. Sort of shown on sketch. The panels under neath are 3mm and add some ridgidity The top bar is 32mm galve and the uprights are 2 40mm agles welded to make a box section with 6mm walls. One day I will lower the top rail by about 32mm and repaint -dont use supercheap spraypaint Hope this helps -if I did it again Iwould probably mock op the mount plates with plywood so that it would be easier to get the shape right