I saw them in the fall of '66, freshman year at college. He was playing the same two guitars at that time, or at least the 12. He also apparently had a custom Guild made around that time. Not long after that a friend had a guitar he showed me with a letter from Guild. It was a standard body with a custom neck that the letter said was designed for Paul Simon. I'm working from almost a 50 year old memory here, so some things are a little hazy, but it seems that Simon was involved with Guild at one point.
Brad