Some time ago I bought a rebuilt 1969-vintage (it has a red ink stamp) 55A Autolite alternator and installed it on my 428 CJ. I just installed a more correct repro from Dead Nuts On, so I took another look the one I originally installed with an eye towards selling it. I thought I had an alternator for a '69 428 CJ, but now I don't think so - the ink stamped engineering number reads C9ZF-10300-D. It's not an AMK repro (the back of the case has the AUTOLITE marking). The only reference I've found that describes this number is a 1970 MPC, which says it's correct for a 1969 Boss 429 Mustang. I've looked through other forums a bit and found references to a C9ZF-E alternator; my 1970 MPC says that C9ZF-E was used on 1969 Fairlanes and Torinos equipped with a 429. I don't believe the 429 was installed in Fairlanes and Torinos in 1969, though.
So - was the C9ZF-D alternator used on 1969 Boss '9 Mustangs? Pic attached if it helps.