I've recently acquired a decent amount of SunKing material including the updated version of the stretch Eight. The long DC-8 was the first 'Jumbo Jet' and effectively saved the DC-8 programme. The type provided excellent stopgap service with 4 of the major US Trunk airlines, plus was coveted by the supplemental carriers. National flew a pair that filled the gap until DC-10s could takeover. Here's their story:

Incidentally it's crazy to think that these stretch Eights seated 259 passengers while a 737 MAX 10 can get up to 232 in a single class layout.
Stretch Stopgaps: National's Super Sixties
The stretch DC-8 super 61/63s were the first 'Jumbo Jets', indeed Flying Tigers even had that title painted on theirs, and provided not only a second life for the DC-8 itself, but a useful stopgap for airlines looking to increase capacity before widebodie
www.yesterdaysairlines.com

Incidentally it's crazy to think that these stretch Eights seated 259 passengers while a 737 MAX 10 can get up to 232 in a single class layout.