The B-720 also has leading edge devices, Krueger Flaps to be exact, while the 707 had no leading edge devices until the 707-320C that was introduced later than the 720.
The B-707 type rating today shows, "B-707/B-720" much like the 757 and 767 shared rating. The FAA will grant KC-135 military pilots who apply for a commercial certificate the B-707/B-720 type rating for the KC-135 experience, but the aircraft types have interesting differences. For example, the KC-135 have no flight engineer today - and even when they did when the aircraft first came out, the flight engineer on a KC-135 had a much different job technically speaking versus a civil FE on a B-707. The -135 FE had no flight engineer panel, but rather manupulated switches on the simple yet different overhead panel between the two pilots. The different fuselage widths/shapes/sizes and different systems reflect the different needs of the military versus early long haul airline operators.
More fun trivia.