Typo. I meant the Boeing 707-220ER.
707-220
The 707-220 was designed for
hot and high operations with more powerful 15,800 lb (70.3 kN)
Pratt & Whitney JT4A-3 turbojets. Five of these were produced, but only four were ultimately delivered, with one being lost during a test flight. All were for Braniff International Airways and carried the model number 707-227; the first entered service in December 1959.
The WTC Design was completed in Jan, 1964. It assumed the largest and heaviest aircraft then flying. That was the Boeing 707-220ER.