Boeing 707-320C
Wasn't the reason the 747 was designed with nose loading capability that at the time Boeing were pitching for a large military transport, which was actually awarded to Lockheed for the C-5A? As an aside I recall that when Seaboard World operated the 747-200F the idea was to be able to load 2 x 20ft ISO size containers side by side through the nose, don't know if that ever happened though.
At the time of the 747 development, Boeing was hot and heavy into the SST development (and in fact Sutter had to fight dearly for resources since most of the money and manpower was devoted to the SST )(same thing happened during the 747-8 program - most of resources went to the 787 - there was great satisfaction among the 747-8 team when we certified before the 787 despite the 787 getting most of the resources and a several year head-start). Further, as Asturias notes, it was believed the 747 would have a relatively short shelf life as a passenger aircraft as future long range travel would be by SST. Hence the 747 was provisioned to make a good freighter from day one (something Airbus failed to do with the A380).
BOAC bought a 707-379C G-AWHU off the shelf (already painted and built for Saturn but their order for 3 was NTU) to urgently replace the lost G-ARWE,
Likewise G-AYLT was the last 707 bought by BOAC to replace the SVC10 lost at Dawson's Field, Jordan.
As WHBM outlined >
The 707-320B has the range benefit over the -320C but many Legacy airlines bought both types.
The -320C at the time was chosen early on by a lot of airlines to also enable MAC work (US Troop movement charters)
The Vietnam War was in full swing - However the trend changed to ordering the DC-8 63CF series especially for US supplemental charter airlines.
Some airlines cancelled their 707C orders to buy the superior DC-8.
Trek Airways had ordered a new 707-350C from Boeing for its JNB-LUX route in association with Luxair, but the aircraft went from the production line to SAA to replace their brand new 707-344C 'Pretoria' lost at WDH in 1968.
Likewise G-AYLT was the last 707 bought by BOAC to replace the SVC10 lost at Dawson's Field, Jordan.
As WHBM outlined >
The 707-320B has the range benefit over the -320C but many Legacy airlines bought both types.
The -320C at the time was chosen early on by a lot of airlines to also enable MAC work (US Troop movement charters)
The Vietnam War was in full swing - However the trend changed to ordering the DC-8 63CF series especially for US supplemental charter airlines.
Some airlines cancelled their 707C orders to buy the superior DC-8.
Trek Airways had ordered a new 707-350C from Boeing for its JNB-LUX route in association with Luxair, but the aircraft went from the production line to SAA to replace their brand new 707-344C 'Pretoria' lost at WDH in 1968.
well that Air Pictorial goyt it a bit wrong - "likely to be the last long range, sub-sonic jet airliner in the Western World"...................... 
As I understand it, it wasn't just the range on Tokyo to Moscow itself that was marginal for a BOAC 707-320C. The diversions and service recovery allowed at Moscow were pretty poor, so I believe they always carried fuel for Helsinki, and in fact operationally preferred to go just a bit further still to Copenhagen if possible. At least one diversion made it as far as Amsterdam I once read - did anyone actually get right through to Heathrow ?
I imagine that the reason that airlines bought 707-320Cs rather than -320Bs was the greater resale value, The future of passenger travel in the early/mid sixties was supposed to be supersonic, which is why the 747 was designed to have the capability for nose loading of main deck cargo. Ultimate payload range was not really a factor in those days as so many long haul routes were multi stop.
