Along with the F-16s there was a KC-135, which is a variant of the now long-gone 707s. The USAF has managed to keep these flying now since the mid-1950s by buying up civilian airline 707s as they were retired and cannibalizing them for parts. The longevity of some of these airframes is incredible, considering most passenger planes now are rarely more than 15 years old!
To get the higher bypass ratio wouldn't it make more sense to mount four larger engines, in bigger nacelles, instead of eight small ones? Bypass ratio and thus fuel economy is achieved by making the fan disc physically larger.
I listened to a podcast about the B 52 recently. Four modern engines definitely would provide enough thrust however they determined it was too much effort to convert it. All the controls and systems are designed for eight engines.