Comically one of the most desirable defenders has a BMW 6 cylinder
and the Rover v8 was used in, uh... Everything.
The Rover V8 is one of the most legendary engines in the automotive industry and has been used in several cars over the years.
www.hotcars.com
The chevy 250 straight six was in everything from bread trucks and pickups to camaro's and chevelles.
The myth of "car engine vs truck engine" is nonsense.
It's not a myth - there are car and truck engines, specifically designed as such....like some of the obscure 'big block's' like the Chevy 366, long stroke, heavy 4 ring pistons, etc.
Car engines are designed to a very aggressive price point and for fuel savings these days....those ones you list are basically overbuilt truck engines put into cars, which does not happen in today's world for a number of reasons.
The Dodge Ram 6.4 truck engine is different than the 6.4 in the cars.
Ford 7.3 is not put into cars.
Chevy 6.0 is trucks is very different than cars.
Some of the Chevy 350 V8's used for industrial applications had some tweaks vs the ones you saw in passenger vehicles.
I'm sure the manuf. that use the same engines across platforms test them to the most extreme use case (say using in heavier truck for testing). I think the Toyota V6 3.5L probably falls into this category, it's used in minivans, sedans and also the Tacoma.....but I am sure it passed durability tests associated with the Tacomas life cycle.
The BMW B58as far as I know was only used in lightweight passenger cars....doesn't mean it couldn't work well in the IG, but it's original design intent was never an offroad SUV or industrial type durability in mind. The biggest issue I see is it was never designed with maintenance in mind like you'd find on most rigs, even modern ones like domestic HD pickups / Toyotas let alone old school Rovers / Landcruisers.
The notorious example are the Mercedes Gwagon & sedans....they used the same diesel 4/6 cylinders. They were industrial engines WAY overbuilt for cars which is why the cars last 500k miles and are easy to rebuild. That concept of over-building and ease of maintenance of vehicles doesn't exist outside of the HD Truck market and some select SUV's like the Landcruiser/Patrols these days....IG has potential, but not from a engine perspective (IMO)