Thanks for the lead - I am chasing this up, but its not a common title !.
I have also submitted a request to USAMHI Research Centre (December 2010) for photocopies of any relevant pages from the work "The 373rd Engineer General Service Regiment in World War II", which is listed as being in their collection. I am told that there is a piece on building of G-40 with photographs (but whether the photographs relate to G-40 (Sully) remains to be seen - if I am lucky that is). If anyone has a lead - or better still a copy - of this work, perhaps they could get in touch so that I can confirm my presumption.
Much of the land occupied by G-40 and its associated tented camp remains undeveloped, and any buildings that may have existed have been removed. A group of us in Barry intend to have a "poke around" this Summer, if we can get permission.
I would be delighted to hear from anyone who has any connection to G-40 as I am trying to put a history together as there is no recognition of the presence that the American Armed Forces made to the town between 1942 and 1944 - although a fair number of Barry "girls" became "GI brides" - my Aunt being one of that number.