You can stuff them but they will rub on bumps or when turning and hitting a bump. If you are ok with that then stuff em. 6" of lift is recommended for 35x1250 if you want 37's they will rub. I run 37x13.50x16 with 7" of lift and they hit the fenders when I articulate or hit a bump while turning6 inches more? I thought you could stuff 37's under a 6 inch lift period.
Regardless you'll need more lift
In my opinion fender trimming is a last resort... Sure fender trimming will work for the body but it may not work for the inner fender well or clear the radius arm at full crank depending on the back spacing, especially with a 12" wide rim... There are many ways to stuff tires under a truck. Some ways are half ass or on a budget and other ways are the recommended. As for your 4", 33x12.50 is the recommended 36's is pushing it and no way on 37's. once you go past 33's it gets tricky because the late bronco's have the smallest fenders of any ford truck :banghead The tires may stuff under but will rub or cause body damage at the first sign of articulation. If you trim the fenders they may not hit the body but will rub on the inner fender or radius arms when off roadingwhat about fender trimming? any reason that wont work? not starting an argument just wondering. (i want to run 37's on my 4in)