Looking over at BG, it appears to me that the "welded-on washer" part they mention is the cupped waasher in front of the forward, big bushing. If you get the sequence right (cupped washer, big bushing, bracket, spacer, small bushing, flat washer & nut) there should be about 3/8"-1/2" of thread exposed on the end of the radius arm. If you can't get that arm to pull back far enough, and the nut is flush with the end of the arm, you may either have the sequence incorrect or something is not properly seated. It's often helpful to use a come-along to pull the frontend to the rear so it gives you the right mounting of the bushings. When you go to get a new frontend alignment, you can have the shop check these out for you, and check the torque on the rear nut. The arm may even move rearward slightly when you first drive the bronco, and it's a good idea to check the tightness or torque a few times until it settles in.
As for the rear pinion seal leak, it depends on what axle you have (9" or 8.8") as to ease of replacement. Might put the year model and specs of your bronco in your signature, JSM84