Interesting, I started off in commercial vehicle(lorries in the UK) servicing and the US influx was large in the 70's
I think Chrysler Motors bought out what was the Rootes Group, stirred things up a bit. They brought in high-speed diesels, unlike the slow stuff we had.
Nice to hear Cummins are still going, thought they would have disappeared into GM years ago. Well respected, and reliable, oil tight if I remember well.
Forgot about Perkins,high-speed, but not very reliable
https://en.wikipedia.org/wiki/Perkins_Engines#High-speed_diesel_engines
Generic 70's diesels:
https://en.wikipedia.org/wiki/L._Gardner_and_Sons#Post-war_diesels
Should mention Leyland, probably the largest commercial vehicle builder in the UK for awhile.
https://en.wikipedia.org/wiki/Leyland_Motors
At that time manufacturers were offering chassis with a selection of engines.
Cummins, Perkins, Leyland, Rolls-Royce(nobody bought those, they were useless, except the military)
And one of the strangest diesel engine.
Three cylinder, six pistons, horizontally opposed, underslung crank-shaft at right angle to the cylinders with rocker-arms. Direct injection, supercharger, forgot, its a two stoke!
https://en.wikipedia.org/wiki/Commer_TS3
Gets dafter...
https://www.youtube.com/watch?v=OTmkO6D0OWI