JW411,
The 707-138B has not much in common with the -320B, except the engines.
-121 modified wing with additional center tank fuel, and a shorter fuselage, approximately a foot shorter than a 720.
Maximum all economy seating of 166.
Having said this, it had a twelve hour endurance, quite a long way for the time.
Built specifically for QF.
Personally flew these for awhile, good airfield performance.