Without wishing to start an argument on such a thread, there were more than 7 airframes with the 301 series engines.
A quote from aeroflight.co.uk
The production line switched over to the Vulcan B. Mk 2 version on the 46th and subsequent aircraft. The first production B. Mk 2 (XH533) flew on 19 August 1958 with Olympus Mk 200 engines. From 1960, Olympus Mk 201 engines of 17,000 lb (7,711 kg) thrust were introduced. By 1963, Olympus Mk 301 engines of 20,000 lb (9,072 kg) thrust were being fitted (from aircraft XH557), but no engine retrofit for earlier B. Mk 2s was attempted.
May the memories of the crew always be present in our minds.