The journal, Integrative Psychological and Behavioral Science, has published a series of papers on the relationship between Harry Harlow and John Bowlby. The are well worth reading. Five of these papers are published online as open access articles.
Introduction to the special issue:"When Strangers Meet": John Bowlby and Harry Harlow on Attachment Behavior
Frank C. P. van der Horst, Helen A. LeRoy and René van der Veer
Loneliness in Infancy: Harry Harlow, John Bowlby and Issues of Separation
Frank C. P. van der Horst & René van der Veer
Rigorous Experiments on Monkey Love: An Account of Harry F. Harlow's Role in the History of Attachment Theory
Stephen J. Suomi & Frank C. P. van der Horst & René van der Veer
The Monkey as a Psychological Subject
Harry F. Harlow
Harry Harlow: From the Other Side of the Desk
Helen A. LeRoy
I've commented on this topic previously and will again at some length.