If you want an FD body with an EOS ethos, that's the T90.
Even if you could attach the mount and trim off 2 mm somewhere (assuming it you could do it precisely enough to maintain alignment) without the lens clipping the mirror, you would have to add a pin to engage the aperture lever and stop down the lens, and then use it in stopped down mode only. There aren't really many reasons to do this unless you want to convert one of those bodies that we don't talk about on APUG to FD. If you just want to use some exotic FD lens that would be absurdly expensive in EF mount, then it makes more sense to get an FD body just for your FD lenses.
Regarding the Canon FD-EOS adapter, there was a non-optical adapter called the "macro adapter," because it didn't allow infinity focus, so it only made sense to use with macro lenses, and there was an optical adapter that acted like a 1.2x tele-extender and had protruding elements, so it only works with lenses 200mm and longer that have enough space between the rear element and the mount to make room for the protruding elements. It didn't crop the image, because you still use the whole 35mm frame, but it enlarged the image, like a 1.4x extender or 2x extender.