I flew the DC-8 as passenger and cargo airplane in the 1980s...
Must say that it was a decent airplane (although I was a Boeing guy)...
Did not like the DC8-50 and -61. Flew these very little.
But the 62/63 and 73 were great machines with decent payload.
The 71 was ok - but only as passenger airplane.
xxx
The story our friend
727gm mentions above is quite correct.
However it was not for building additional DC-8.
It was to convert more 60 series into 70 series with CFM nacelles-engines.
MacDac hoped by stopping DC8-70F production to sell more DC-10F...
xxx
Happy contrails