Fantastic story, Bruce. It's hard to believe 40 years have passed since you and your Rickenbacker first parted company. You hear plenty of stories about players being re-connected with instruments sold in earlier years, but not forty years!
Bruce, I believe there are a number of us in your (our) generation who would love to find our '60s Ricks that we have since traded away, sold or worse. What makes your story so unique is that the guy to whom you sold it brought the guitar to you. You probably never would have been able to identify it otherwise. I had a 360-12 MG for several years in the '60s (I believe it was a 1966) and traded it to a friend during college, who sold it. Although it was a great-playing guitar and I had a blast with it, back then it was "just a guitar." I never kept a record of the serial number, never took off the 'guard to see what was underneath, etc. I just played it and occasionally changed the strings.
Good for you two to be reunited after all these years!