Would the engine power available at the time have allowed for a wide body VC-10 with a cabin diameter matching say today’s Boeing 767 on the VC-10 cabin length?

If so, is there a market at the time for such an aircraft?

Vickers prepared a number of schemes in 1964 utilising the basic VC10 structure in a number of interesting ways. “Vickers Aircraft since 1908” (Putnam) has copies of several drawings including two which had two VC10 fuselages and could accommodate 300 or 450 passengers (powered by either 4 or 6 RR Medway engines mounted at the rear between the two fuselages). Another 300-seater was a double-decker with two paired RR Conways beneath each wing and a low-set tailplane. A more recognisable double-decker would have been powered by three RB178-14 “aft fan gas generators” and would have accommodated 295 passengers. They also proposed a military transport with bulged nose section, area ruled fuselage and front loading doors beneath the cockpit.