One of the most intriguing concert information I found, years ago, was that Simon & Garfunkel played at a concert of Frank Zappa with The Mothers of Invention. They performed both as Simon & Garfunkel, but opened the show as ‘Tom & Jerry’ singing Everly Brothers hits. A strange combination indeed, Zappa with Simon & Garfunkel. There’s no real evidence of this fact, by concert bill or review, but you can read about it in The Real Frank Zappa Book and on the internet of course. Some sources inform us with the concert being held in May 1967, September 1967, even Frank Zappa talks about 1967. But it is m0st likely to have taken place in 1969. In the interview with Jospeh Fernbacher, he makes it look like it had been more than just one concert.
Anyway, here’s some of the material, for further reading, found on the net:
From The Real Frank Zappa Book: Tom & Jerry
I was in Manny’s Musical Instruments in New York sometime in 1967, and it was raining outside. A little guy came walking in, kind of wet, and introduced himself as Paul Simon. He said he wanted me to come to dinner at his house that night, and gave me the address. I said okay and went there. As I walked in the door, Paul was on his hands and knees in front of what appeared to be a Magnavox stereo — the same model preferred by “the Stumbler” from Sun Village. He had his ear right up to the speaker, listening to a Django Reinhardt record. Within moments — for no apparent reason — he announced that he was upset because he had to pay six hundred thousand dollars in income tax that year. This was completely unsolicited information, and I thought to myself, If only I could earn six hundred thousand dollars. What did you have to earn in order to have to pay that much tax? Then Art Garfunkel came in, and we talked and talked. They hadn’t been on the road in a long time, and were reminiscing about the ‘good old days.’ I didn’t realize that they used to be called Tom & Jerry, and that they once had a hit song called “Hey, Schoolgirl in the Second Row.” I said, “Well, I can understand your desire to experience the joys of touring once again, and so I’ll make you this offer. . . we’re playing in Buffalo tomorrow night. Why don’t you guys come up there and open for us as Tom & Jerry? I won’t tell anybody. Just get your stuff and go out there and sing ‘Hey, Schoolgirl in the Second Row’ — just play only your old stuff, no Simon & Garfunkel tunes.” They loved the idea and said they would do it. They did the opener as Tom & Jerry; we played our show, and at the encore I told the audience, “I’d like to bring back our friends to do another number.” They came out and played “Sounds of Silence.” At that point it dawned on everybody that this was the one, and only, the magnificent SIMON & GARFUNKEL. On the way out, after the show, a college-educated woman walked over to me and said, “Why did you do that? Why did you make fun of Simon & Garfunkel?” — as if I had pulled some kind of cruel joke on them. What the fuck did she think had just happened? That these two SUPERSTARS had dropped in out of nowhere and we had FORCED them to sing “OOO-boppa-loochy-bah, she’s mine!”? Simon & Garfunkel Clark Gymnasium, SUNY, Buffalo, NY, May 2, 1969 FZ & Peter Occhiogrosso, The Real Frank Zappa Book, 1989, p. 98-99
Billy James, Necessity Is . . ., 2000, p. 73
I was in Manny’s Musical Instruments in New York sometime in 1967, and it was raining outside. A little guy came walking in, kind of wet, and introduced himself as Paul Simon. He said he wanted me to come to dinner at his house that night, and gave me the address. I said okay and went there. […] Then Art Garfunkel came in, and we talked and talked.
They hadn’t been on the road in a long time, and were reminiscing about the ‘good old days.’ I didn’t realize that they used to be called Tom & Jerry, and that they once had a hit song called “Hey, Schoolgirl in the Second Row.”
I said, “Well, I can understand your desire to experience the joys of touring once again, and so I’ll make you this offer . . . we’re playing in Buffalo tomorrow night. Why don’t you guys come up there and open for us as Tom & Jerry? I won’t tell anybody. Just get your stuff and go out there and sing ‘Hey, Schoolgirl in the Second Row’–just play only your old stuff, no Simon & Garfunkel tunes.” They loved the idea and said they would do it.
They did the opener as Tom & Jerry; we played our show, and at the encore I told the audience, “I’d like to bring back our friends to do another number.” They came out and played “Sounds of Silence.” At that point it dawned on everybody that this was the one, and only, the magnificent SIMON & GARFUNKEL.
Joseph Fernbacher, “Mothers Of Invention,” The Spectrum, May 7, 1969, p. 8 :
“I remember the band going on the road to Buffalo, NY for a weekend, and Simon and Garfunkel came along for some fun!” [Bunk] Gardner recalls. “We did a lot of bizarre stuff in the hotel and in our rooms that Simon and Garfunkel filmed, like Motorhead and I demonstrating the ‘Buster Crabbe’ for them. Later on the concerts, we would introduce them as our mystery guests, and while they sang, we did our usual weirdness right along with their singing. It sticks out in my mind because I remember it was my birthday.”
A weating body of students sat through the first lecture of a new science course Friday night in Clark Gym. The visiting professor was Frank Zappa – accompanied by his nine mothers. […]
Kicking off the evening were a pair of aspiring young singers called “Tom and Jerry.” […]
Actually this group was none other than those fantastic leaders of the folk world, Simon and Garfunkel. They just happened to be in the area at the time and decided to visit Dada Frank and Company. To say that one’s mind almost stammers at the sight of lanky Art Garfunkel and pudgy Paul Simon weaving their way between Frank Zappa and his music is an obvious understatement. After doing a set Simon and Garfunkel gracefully left the stage to the Mothers of Invention.
The Mothers began with a heavy piece taken from their latest lp entitled “Uncle Meat” — so is their new lp. […]
After picking myself off the floor, the Mothers brought back Tom and Jerry, who did some more Everly Brothers’ tunes and wandered about the stage looking lost. They did do a stirring rendition of “Sounds of Silence,” circa 1950, complete with shu-bops and dong-dongs, and “Oh. baby lets do it once in silence. ”
Obviously tired and sweaty, the Mothers wanted to split. The audience didn’t like this. So Zappa put us into a bind. If we clapped and jumped up and down, we made asses out of ourselves and if we didn’t do anything, they would leave. So we made asses out of ourselves. Zappa came back, but was obviously angered.
[…]

I love this story. I do think 1967 might make more sense, because wouldn’t they have been too famous/recognizable by 1969 to pull it off?
Well it was Frank Zappa who wrote about in that book and mentions 1967. So it would make sense it was 1967. But he mentions the ‘famous Simon & garfunkel’. I wonder how famous S&G would have been in May 1967? I mean, sure they were well known, a couple of hit records and 2 albums out. But wasn’t it that untill The Graduate was released that they became very very famous? And the fact that it is mentioned that they hadn’t been on the road for a long time, makes 1969 more logical to me.
Anyway, I have contacted the Library of the University of Buffalo and hopefully they will come with the information needed.