FD to EF mount basic instructions
Using only a Kenko extension tube set, small bolts/nuts, drill, sander/grinder and a dremel tool I was able to construct these nice adapters to take advantage of better optics in the original Canon FD teleconverters over the readily available low cost Ebay adapters.
Update: I added the best (in my opinion after trying a few) available focus confirmation chips. They are branded "Dandelion" and can be purchased from ebay seller ml-gvalt in Belarus who ships fast with no border issues on the few shipments I've gotten. What sets these chips apart is that you can program them from your camera to report back whatever aperture, focal length (so exif data is correct and metering in auto modes is helped), and emulates an autofocus lens so a camera can be set to only take a picture when it thinks focus has been achieved allowing one to chase a flock of birds with the shutter pressed and focus being manually manipulated and only have pics taken when they come into focus.
NOTE: THERE IS A BETTER WAY, the 600 and 800 lenses can focus to infinity without optics by removing one screw and using an ultra low profile metal adapter.