It's been many years now, but I do remember Mark Hildebrand when I was a member of Bethel Lutheran in Cupertino, CA.  I most remember him for singing 'Birthday of A King' at Christmas (with the choir, which I was a part of).  When I hear that anthem today, I still think of Mark.  His quartet also sang for us at our company picnic in the late 70's.  Sincerely, Becky Anderson Andersen