1. Decide on what I.D. you want. 2. Google search "can, cup, tumbler, etc." with that diameter...... or maybe you already have some empty containers in your shop, like butane bottles or whatever. 3. Cut the holes in the fender(s) too small to start and work up to 'just right'. 4. Once you have the first "can" trimmed how you like it, wrap paper around it and cut a pattern for the other(s). 5. Set your Ford for the finished stance and use a small bubble level in the "cans" to square them level.
They have been over-done, but the fact is they can also look good if done right. The shift wizard has some excellent advice here. I think Frenched into 37-40 fenders could be a great application.
Use the same procedure as you would to French an antenna in, I learned this technique here and used it in my car when I built it. See my project thread for easy to do pics. Good luck on your ride
I have them on my 40 truck, but couldn't find an image, but this was on the HAMB somewhere and I stole it