Sad... My dad was flying Boeing 720 (A:s and B:s) 1970-1976 as F/O and 1976-1987
as captain (before head 3 year experience of propliner DC7 later 10 year with Airbus A300 and A320. He flew for the danish chartercompany "A/S Conair of Scandinavia"
(Con.. stood for Consolidated.. not Convict...)

I think that this aircraft was the most good looking of all aircrafts through history,
the four engines and the antenna mede it a beuty. Number two is then of course it's cousin Boeing 707. The close looking (and close concurrent) DC8 had a differen windowsetting in cockpit (whith a not so good looking "mid-window")

But the Boeing 720 was a real noicemashine too. It sounded more than two Boeng 727
for instance. The hydraulic system on board was mainly for the gear´-up and gear-down functions. All rudders were by wire ! It flew higher than most other aircraft up to 43000
feet were no problem. Only the Concord could fly above.
The skeleton were partly wood (!!!)

It also had no APU and were depending of compressed air from the ground personel to get the engines running (wich was a truly complicated matter)
Only the first engine (usally number 4) was depending of ground personel - after that the other engines could be started by the running one. But usally ground helped with all four.
In air (if all engines shold stop) it was possible to restart engines by use of a
wind mill. Souch event occured probably never whith Boeing 720, but I've
red about a 747 Jumbo whos all four engines stopt when vulcanic aches came in
to the turbines. But by high altitude and godd work by the captain an crew all the
engines were restarted