Steven P , Mar 05, 2011; 06:20 a.m.
It's not that hard to do it yourself.
Flip up the Ai prong on an F3, mount the lens, score a mark on the lens' aperture ring. Remove the lens mount. (Those screws are usually pretty tight.) Aperture ring pulls right off. Remove the bunny ears and use a small file to notch out the area needed, including mounting clearance. The ring is aluminum and easy to form. Rough file the location, and finely work back to the exact place where the ring meets the tab. You can even lightly paint or use a sharpie to blacken the filed area.
I've done several in the past and it doesn't take long. Having seen photos of some lenses done "professionally" (I don't remember the guy's name.) my "hack job" actually looks better. The only thing missing are the aperture numbers for the finder window.