Hola b377 -
xxx
Doing this from memory.
The JT3D versions appeared quite early in the 707-720 production history.
Quite a few old "straight pipe" JT3C powered were reengined with JT3D.
xxx
If I recall well, American Airlines reengined they entire 707-123 and 720-023 fleet.
These were "converted engines", installing the fan on the core JT3C-6 and 7.
The engine designation became JT3D-1-MC6 or MC7 (MC= Major Change).
These were both 17,000 lbs/thrust engines.
I think TWA converted some 707-131 airplanes. Cannot recall.
Qantas converted all their 707-138 to fans. Travolta's is one of these.
Western Airlines 720-047 all got (I think) converted.
I cannot recall what happened with Northwest and Continental.
xxx
However, quite a few "straight pipe" 707-100 remained with original engines.
United and Aer Lingus 720 remained with their original JT3C-7.
They were first to be retired in the early 1970s.
I do not recall, nor can document any 707-300/400 converted to fans.
They kept their JT4A/Conways for their entire flying history.
The 707-100B and 707-300B started to be delivered in 1961 or 1962.
Most 707-100B had JT3D-1, and 300 were JT3D-3B (or later even -7)
xxx
You better look on the 707-720 production list for accurate details.
Gave all my 707/720 books to wannabees... so cannot help any further.
xxx
Happy contrails
P.S.
Sure, the Conways were fans... but the bypass ratio quite low.
Just like the 727-737-DC9 JT8D... I would call them "bypass" instead.