Simon & Garfunkel-"Cecilia"

I have a later CD pressing (late 1990s) of S&G's Greatest Hits and, even by the standards of the pre-remastered Columbia CDs, it's one of the worst sounding CDs I have ever heard. Extremely high generation source tapes. It does have a full stereo "Cecilia".

Mono 45 version

Nope. As long as Paul Simon walks this earth, I'm willing to bet that this will never appear on CD or in digital form.

The vinyl dub that I have runs 2:38.

Hit 1970 stereo mix

I would think that any CD released before 1997 would have the original stereo mix, but there are different amounts of added stereo reverb on many of them. Not just the echo effect of the drum track, but real stereo reverb on top of that. I don't know what was on the 1970 vinyl LP.

The 1990 original CD release (Columbia C3K 45322) of 1981's Collected Works has what I'd call a medium amount of added stereo reverb. Warner Brothers' Paul Simon 1964/1993 (1993) is a differently-EQ'd digital clone of Collected Works, and therefore also has a medium amount of added stereo reverb.

The 1985 original CD release (Columbia CK 31350) of 1972's Simon And Garfunkel's Greatest Hits has what I'd deem to be a life-threatening amount of added stereo reverb. It's a big soupy mess.

Others:

I don't have the 1985 original CD release (Columbia CK 9914) of 1970's Bridge Over Troubled Water album.

The 1983 (?) original CD release of 1981's The Simon And Garfunkel Collection almost certainly has pre-emphasis, which boosts the very high end unnaturally. Even with the high end boost, it sounds pinched and weird, like the mastering added noise reduction that sucked all the life out of the recording. It's not the digital-era noise reduction, which shows artifacts on the fade, but it has the same effect of deadening the whole recording. I avoid this collection when I can; it's the one with two guys on the beach that are hilariously not Paul and Art. Literally everything is wrong with this disc.

Non-hit 1997 stereo remix by Vic Anesini

Vic Anesini remixed everything on Columbia Legacy's Old Friends box (1997). The new mixes sound stellar, as you might imagine, as Vic Anesini is superb at what he does. The left and right channels are out of synch by 1 sample, which is easy to fix. The opening drum track is centered (after you resynch the L and R channels), and there's no stereo reverb. The song is basically mono until 0:05 when the shaker comes in slightly panned. When the vocals start, the only instruments that have any panning are the shaker and the vocals. This 1997 mix has essentially no added stereo reverb.    

Old Friends fades the last two beats of the song to silence. There are level-adjusted digital clones on:

• Columbia/Legacy's Best Of (1999) - fades the last two beats of the song to silence
• Columbia/Legacy's Bridge Over Troubled Water (2001 reissue) - last two beats are not faded to silence
• Columbia/Legacy's Essential (2003) - last two beats are not faded to silence
• TM Studios Goldwav track no. 00001008 - fades the last two beats of the song to silence

Legacy's Over The Bridge Of Time - A Paul Simon Retrospective (1964-2011) (2013) seems to use the 1997 mix, but fixes the left/right desynchronization. Well done!

My recommendations

For the 1970 stereo mix, I guess it depends on what's on the 1970 vinyl LP. I'm hoping someone will post what was on the 1985 original CD release of Bridge Over Troubled Water.

For the 1997 stereo remix, you can fix the desynchronization yourself on any of the above, or just go with Legacy's Over The Bridge Of Time - A Paul Simon Retrospective (1964-2011) (2013).