obscure Canon -> Leica thread mount adapter question

[pgs@pa.dec.com (Patrick Sobalvarro)]

I have a question about an obscure lens mount adapter.  It's a "Canon
Lens Mount Converter A".  The store claims it's a converter from Canon
FD mount to Leica thread mount.  If I were sure that this were true I
would buy it.

I worry that the store may be mistaken, however.  I have a piece of
documentation, namely Viewfinder (LHSA magazine) Vol. 28, No. 2, 2nd
quarter 1995, p. 35, showing a "Canon Lens Mount Converter B," which
is supposed to adapt any breech bayonet Canon lens to Leica thread
mount.  Now, my understanding was that the difference between breech
bayonet and FD mounts was in the presence of an aperture coupling pin
(not important for a rangefinder) and the presence of a locking ring
on the lens (not the mount), but that the two systems are otherwise
interoperable.  So why would there be two different "Canon Lens Mount
Converters" then?

Anyone have any idea whether "Canon Lens Mount Converter A" is really
a Canon FD mount -> LTM converter?  I would check by examining it
directly if I could without buying the converter, but the store is a
mail order operation thousands of miles away.

- -Patrick

P.S. The only reason I'm interested in mounting a Canon FD lens on an
     LTM body is the picture of the Canon 7.5mm/5.6 fisheye mounted on
     an MD on the above-mentioned page of Viewfinder.  It's just so
     weird, I want to try it.  (Not that I was thinking of buying that
     fisheye lens anytime soon.)