I disagree about the 6, in that it is gasoline.
The original chain-driver 4 cylinder “turbo”* diesel is an amazingly tough little engine. It’s the same Perkins diesel found in London Taxis, de-tuned even more. Basically bullet proof.
* it’s barely boosted.
I’m familiar with the 4 cylinder, 85 HP Perkins used in construction equipment, and it’s pretty good on diesel.