I am not sure what a "Prep" sight is. On my GP rifle I thinned the front sight down from .125 to .100 or 1/10th of an inch. That made it easier to target shoot with.
On the new Pedersoli Scout Rifle I just got the black front sight was hard for me to see and disappeared on about anything I pointed it at. So using a toothpick I put a thin coat of white acrylic paint on and when that dried I put a coat of lime green it it. Now it jumps right out at you. Not very traditional but I don't care. I can't shoot what I can't see.
On the CVA I kentucky pistol I built a few months ago the rear notch was too narrow. So a little work with a needle file and its far easier to see the front blade and I can see a little light on each side.