I don't know much about Howard Heitmeyer. He was a close colleague of H.R.'s at one time and seems to have spent most of his career teaching. There is a an article, Unknown Greats - The Great Howard Heitmeyer, Guitar Player, March, 1989, p. 36, that provides a few details about him. Also the site Howard Heitmeyer is a source of some videos he made about playing classical guitar.
There is an interview with Howard Heitmeyer published in Just Jazz Guitar, November 2007, namely, An Unknown Great: Howard Heitmeyer by Craig C. Brandau, Just Jazz Guitar, November 2007, 138-144.