I do not know the actual facts of the situation that motivated some pickup truck makers to use V8 diesel engines for power. I think possibly they initially viewed Chrysler as a vehicle maker on the bottom end of the big three spectrum and decieded the I-6 would only convince public consumers that the top two's old fashioned competition had completely gone off the modern progressive track. The auto makers had for decades been brainwashing the population that V8 power was the latest greatest techology. GM/Ford decided the deceived public was in the majority and would take to the V8 diesels as a wise choice. What GM and Ford did not count on was that the V8 configuration would show its inferior physical limitations that engineering technology could not overcome to make it equal or superior to the I-6. Advances in technology help the V8 function satisfactorily to a degree, but natural laws of physics make it easier for Cummins to keep the I-6 ahead of the V8 by Cummins using those advances in technology. The V8 diesel is a high reving road runner on level ground that will be ahead of the I-6 without tall gears. The I-6 shines when heavy loads have to be hauled.

 

Remember GM's first failed attempt at providing a V8 Diesel (The 5.7 V8 Diesel that was offered from 1978-1984) ??

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Remember with the balance of engines that we have both power pulse vibration and spinning mechanical vibration. A 90 degree configuration cancels out each of the single cylinders mechanical vibration and runs smooth (imagine 4 V2s next to each other). With side by side rods on each throw they aren't perfect, but close. 90 degree V8s are one of the smoothest designs ever. 45 and 60 degree engines are problem designs like Harleys and V6s. Unless of course, they have balance shafts.
Power pulse vibration seems to get better and better with more cylinders or at higher RPM, as long as they are firing at even degree intervals. Six in-line is better than five and five is better than four. 90 degree V6s don't fire evenly and 60 degree V6s are mechanically out. You either get uneven firing or out of balance mechanicals. Depending on how the crank is designed, these problems can be reversed (offset big end bearings on each throw).
45 degrees is even worse (Harley).
Don't get me wrong, I like my Harley, but compared to my 90 degree Moto Guzzi twin it just thrashes around. Not from power pulses but from mechanical vibration.
As far as the strength of a V8 crank vs an I6 crank, yes the six has a bearing between each rod but it's also a lot longer. So there is more torsional stress. Each design can be very strong it just has to be sized appropriately. Small block Chevy and Dodge V8s can take an outrageous beating. One of the most durable engines I've ever seen is the 318.

Wetspirit

 

But the 45 degree V-twin, with the shared power stroke and crankshaft journal, is the greatest sounding engine of all time.

I mean, that's worth quite a lot.

 

It is, and they haul **s too.

Wetspirit