For those not already aware, about a year ago Ed Mika (Ontarian on Flikr) began development on a new glassless FD-EOS adapter (with AF confirm) that allows focus to infinity on 600mm and 800mm FD lenses, and longer focus than any other glassless converter on other lenses (300 feet on 400mm FD, 38 feet on 200mm):
After a few different attempts he has finally finalized the design and first production run. They are now for sale on Ebay for $135:
To use it you do have to mod your lens, but it is supposed to be a very simple and easily reversible mod (Just remove a screw or something).
I just placed my order for use with the 600mm FD I picked up last year. If you have a longer FD lens lying around you should look into getting one yourself.
It works best with the 600 and 800mm lenses because those can "Focus past infinity" just enough to not act like they have a 2.75mm extension tube attached.