Easiest, most popular engine to work on:

Hi wore out, sure, now, but there was time, and I don't want to start another 2 cycle schpiel, but fact was, with old Detroits, if you didn't put a rod through the case ( like I did) the night shift mechanics could usually have your truck ready by morning. ( it didn't go any faster, but at least it was fresh)

 

N14 or Series 60. Mechanical, parts are the issue, especially Cat.

 

The 14L EGR ones might have been. Never toyed with them much. The older 12.7's were electronic unit injectors run off a cam lobe. Common rail fuel systems have a single high pressure pump (like 20k + psi) that supplies a common rail and the injectors are trigged by an ECM pulse that opens the injector.

 

I don't care much for Chevy motors...got to lay on top of the engine dern near standing on your head to reach the dadgum distributor...and then it's a pain in the keester to cinch down without a "special" wrench that nobody carries. Then, you've got a dang sawtooth thingamabobber (IF you're lucky...it's "extra" if you buy a new timing cover, otherwise you're flying blind with NO timing marks whatsoever.

I prefer my Fords, with the distributor right there in the front where you can set the timing real easy, and timing marks right there on the damper.

 

My vote would be the big cam Cummings or the 3406b cat. Very simple and only a few things that could keep them from running.

@Pedigreed Bulldog back in the day we used to paint white out on the timing marks of our small block chevys. It got to where we could time it by making small adjustments and then watching the soot from the exhaust to see if it was too lean or rich. These were somewhat built and cammed motors with four barrel carbs. Nowadays it's a turbo LS stroker that makes more on 4 cylinders than that 350 every thought about.

 

That distributor don't stop the Ford lovers from redoing the firewall just to drop a GM in a Ford body though.... just saying

 

2 top choices as I said earlier. Both have a fairly easy fueling system, especially the DD 2 stroke since it has no injection pump. The ability to pull a hand hole cover off and look right at cylinder is a plus on the 2 stroke
Actually about any mechanical engine beats an electronic engine, when it comes to roadside diagnostics and repair.

 

@OLDSKOOLERnWV

I love that top picture. Look at that spigot style shut off and all the banjo clamps. Fixing a leak on a truck like that requires a pocket knife, a small piece of aluminum tubing to splice and you are back in business. So easy a caveman could do it