picture on Ben Witherington's blog is closer to how I remember him. We've lost a giant in the NT world.
Barrett did not write any monographs or commentaries on Hebrews, but in 1954 he wrote a very influential article on "The Eschatology of the Epistle to the Hebrews" in The Background of the New Testament and Its Eschatology, edited by W. D. Davies and D. Daube.
He also wrote "The Christology of Hebrews" in Who Do You Say That I Am?: Essays on Christology, edited by Mark Allan Powell and David Bauer in 1999.