The blocks are the same (or similar enough) between the old 6bt and the first ISB (which had 24 valves and the vp-44 pump). I have built 6bt motors using the more modern block, crank and pistons before and used a marine head and shitty Lucas CAV pump. Beyond that they don't share much in common.
Most reliable atomotive gasoline engine ever built in the world: - AMC 242
350 and ls are reliable v8's
AMC 4.0 is a great i6
Barra 4.0 as well
On a diesel the injection system is both the most complex and most important part of the engine. To stand back and say "the fuel gear doesn't matter in a conversation about reliability" is like saying "the meat, bun, pickle and sauce doesn't matter in a big Mac" and because you've picked an actual diesel mechanic to argue with all you are gonna make yourself look like a fuckwit
Shh. They don't know the wonders of the redblock.
My old 16v 4age can't even idle becase of people running it without oil and has been gummed up with shit in the coolant by previous owners yet its been running for years of abuse any time I want it. I feel like it deserves to be rebuilt even though I am going 20v for my secondary car. I want to get an old corolla and rebuild and SC it with this old engine it deserves to live on.