You might check the back issues of "Secrets of Speed" magazine by using the on-line index (if there is one) or contacting Charlie Yapp directly via his website:
http://www.secretsofspeed.com/. My issues stop at about 2002, so I can't speak to what's been in the magazine since then. I don't recall anything specific about the Cook head in my issues, but it may have been discussed in the Letters to Editor section.
Jim Brierley's Forever Four magazines are great, too. Maybe he can chime in here with some info.
Marshall