My statement was overly brief. I was referring to actual 707s, the last of which was built in 1978. There have been many derivatives of the 707, and the 707 itself was actually derived from an earlier, military model.
The original 707s did not have enough ground clearance for modern engines, when allowing for the possibility of a hard landing. Newer derivatives, using newer engines, all had engineering modifications which adjusted for this.
If you want to be really specific: the KC-135 is derived from the original Boeing jet transport “proof of concept” demonstrator, the Boeing 367-80 (commonly called the “Dash-80”). As such, it has a narrower fuselage and is shorter than the Boeing 707 jetliner.
For purposes of your argument the specific configuration differences regarding wing/ground clearances are not significant enough to preclude the use of high-bypass turbofans. Besides engines are so much more efficient a modern engine of almost the same diameter could develop quite a bit more thrust. So it’s not so much whether it could be done — more whether it would make economic sense, given the costs of recertification, etc.
Strut compression is one of many considerations. Thrust of the high-bypass turbofans used in the KC-135 is so much greater, the certification weights go up with no added control surface area or wing area, and the 2-engine and 3-engine min control speeds go up.
I know that the KC-135/R and /Q have reduced pod clearances, but their gross weights are much higher too; they could have used even smaller engines had there been no operational requirement to improve the aircraft range and payload.