Tim,
Suggest you try and get hold of a copy of the following DVD, it has lots of info on it on the Brabazon by the people who built it :-
Bristol Aircraft, a century of flight produced by 1st take productions -
www.1st-take.com
also might be worth seeing if you can get in touch with Walter Gibb who was the Bill Pegg's co-pilot on the first flight of the Brabazon and later became it's second captain.
I also suggest seeing if you can get a copy of Sir Archibold Russell's autobiography available from airlife publications ISBN 1-85310-234-2. Also try and contact Oliver Deardon of the Bristol Aero Collection he has lots of contacts who will be able to give you more info on the Brabazon.
PM me if you want to contact him - i have his phone number.
Hope this is of help.
brgds
W.G