I am not going to rehearse the whole story of Garcia's involvement in the album. Matt Scofield does an amazing job of it at deaddisc, and I am sure that Jackson and McNally would shed additional light. (I should just make it a practice to refer to them before ever posting on anything.) Let me just summarize what Scofield says we know and what we don't with a few bullet points, some of them direct quotes from deaddisc.
- Garcia plays guitar on Today and Comin' Back To Me.
- Some sources suggest that Garcia also played acoustic guitar on Plastic Fantastic Lover and My Best Friend.
- Garcia's contribution to Surrealistic Pillow is not easy to define exactly.
- His playing contribution is partly documented.
- Some sources suggest that Garcia was also played on Plastic Fantastic Lover and My Best Friend. To date this remains speculation - any information about documented sources describing other Garcia involvement on this album would be most welcome.
- JG played flattop (presumably acoustic steel) guitar on How Do You Feel (@ ca. 0:58).
- JG did not play on My Best Friend; Skip Spence did. (@ ca. 1:05)
- JG's playing on Today and Comin' Back To Me are confirmed (@ ca. 1:09)
- JG played flattop guitar on Plastic Fantastic Lover (@ ca. 1:11)
- re: Someone to Love JG says "The arrangement on the album is more or less my arrangement. I kinda rewrote it."
From the horse's mouth, so to speak.
Now, of course, it's not certain that his parts appeared on the final product or if, as the lack of credits would imply, they ended up on the cutting room floor. But it may well be him, and in any case we might be able to circle in on some more dates when he was in LA with the Airplane if we know the dates on which the numbers including him were recorded.