Thanks Greg.
In an attempt to get a definitive answer on this pump configuration question, I have been in touch with the guys who would know, namely, the guys who raced them in the 60's.
To that end, I have been in touch with both Jack Sears and Sir John Whitmore. Whilst Sir John, couldn't recall how or when the pumps were operated (it was a long time ago and he stopped racing in '66), Jack has said that the electric pumps ran for the duration and that there wasn't a reserve fuel capacity.
QED
Having spoken to other people, the general consensus is that the race cars didn't have mechanical fuel pumps fitted, which would make sense and fit it with the general practice of the time.
Paul