Only "really" stretched L-1011 I am aware of is the L-1011-300, that reached 207.4 feet (63.2 meters) with two barrel extension, but I doubt that it would be able to carry 400 passengers AND have a very long range. And by the way it was a late '70s proposal. Long range L-1011s had shortened cabins (L-1011-500), since they were aimed at long thin routes (long fat ones were B-747 domain). There was a poorly known presumably long-range Tristar derivative, the so-called CL-1616-8 (strange TDN, by the way, CL-1616 was a completely dfferent aircraft), actually a Quadstar, with four CF6-6D engines, two under the wing and two sideways the tail-cone (DC-9 style). This too was shortened, by 15 feet. That's for the L-1011 (which was a Lockheed-California project). I may add that in late '70s CALAC did the so-called ATX studies (Advanced Transports Exprerimental), that were designated ATX-XXX, where the last three X stand for the passengers carried. The ATX-350, covered by TDN CL-1633, were more loosely based on the L-1011-1, with both cabind and wing estensions. One was long-range (5000 nmi), but it is too late for being the one cited in PS article. Little is known on the Lockheed-Georgia front. The 1970 timeframe could fit with the transonics design GALAC was doing, the largest of which could have carried 400 passengers at 0.98 Mach. And transonics would have been aimed precisely at very long range routes. CALAC did a transonics design, the CL-1244 in 1970, only to be used by Daniel Houghton, then corporate chairman, in a speech (I suspect on occasion of him being induced in the Aviation Hall of Fame). Or, it could be simply guesswork on Popular Science's part....
