Hola BelArg (and others)
Continental only bought five of the early 707-124 model. Two of the five were lost by the mid-1960s and the other three were sold in 1967 to TWA. Then Continental came back and bought many of the fan-engined models.
Western only bought two of the early models (originally ordered by Cubana but embargoed before delivery), which they sold on in 1962 to Pan Am, who lost one of them shortly afterwards and converted the other to fan engines. Western then, again, bough many of the later fan-engined models from new. To be precise there was never any 720-047, only 720-047B.
TWA never converted any of their substantial early fleet of the old "straight pipe" 707s, in fact they later bought Continental's fleet, and ran them all on until the early 1970s.
American converted a huge number of both 707s and 720s, some after less than 12 months service.
Northwest never had a straight pipe Boeing, though they again built up a large fan-powered fleet later. Reason for this was that Northwest were originally a DC8 customer (little-remembered nowadays), they bought five DC8-30s (straight pipe in themselves) and operated them to Asia for a few years, and had another five DC8-50s on order, then cancelled the order, sold the older DC8s to National, and changed completely over to Boeing.
United and Eastern both kept their old 720s as they were until retirement.
The Aer Lingus pair didn't do a lot of work once they bought their first 707-320Cs in the mid-60s, they were leased out a lot and I remember seeing one substituting for an Aer Lingus Viscount from Dublin into Bristol, of all places, which must have been hugely unprofitable.
It is correct that no 707-320 was converted to fan engines whereas many of the 707-120 and 720 were. Must have been some good reason for that, I have always suspected that Boeing did not want to offer such a conversion because they figured it was more profitable to Boeing to require operators to buy whole new aircraft, once they saw how extensive a programme American did.
If you want a complete detailed list, it's here :
http://www.planelist.net/boeing-707.zip
(you'll need WinZip to unzip the file)