Sheldon Black Book has...
#6 Jacky Ickx in chassis 0009
#20 Chris Amon in chassis 0007 - also using 0009 in practice.
Motorsport Magazine states that Ferrari sent two cars to Silverstone.
A new chassis with a lower mounted engine (0009) and Amon's normal race car (0007).
Amon tried both cars in practice and decided he preferred his normal car, leaving the new 0009 chassis for Ickx.
This would agree with the Black Books.
Now look at the photo... you will see THREE Ferraris and not TWO !!
#20 in the background has the lower engine so must be 0009 practiced by Amon and raced by Ickx.
#20T is probably 0007 raced by Amon but with a 'T' for practice.
So what is the Ferrari chassis in the foreground, with the high engine?
Whatever chassis it is it was used in practice by Ickx as #6 because I have photos of a high engine Ferrari with #6 and Ickx driving.
Can anyone shed light on this mystery