I recall reading somewhere that one of the early jets (DC8?) could reverse two engines for descent control.
Correct. Though I have no time flying the plane, I have dozens of hours in the DC-8-63 full sim of the airline I worked for at the time (Worldways Canada). I did many approaches in the center two engines in reverse. As there was no "back" [of the plane] I have no idea what it would have been like back there, but in left seat, it was no problem. I'm not aware that our pilots every did it in flight. I do know that a pilot once tried to back off the gate with reverse when there was no towbar available for pushback. One engine's buckets stuck in reverse and that was that for that flight. There was word that this was operationally very discouraged after that!