I would love to see a small Volvo diesel in pick ups here, and even SISU too.
The Volvo D5 2.4 liter inline 5 engine is putting out somewhere near 420Nm and 220hp. Tuned slightly down for longevity, lets say 180hp and 400Nm, it would be a great engine for a small pickup (Ford Ranger size) if they gave it stiff enough rear suspension so it can tow 7 to 8k pound trailers (3500kg same as most Euro vans)
Personally i dont see the point in a "full size" half ton pickup, their suspension is too light to get any cargo or towing capacity but you drag along all that weight and frontal area anyways... Same thing as when comparing a 2 series Sprinter (not sold in America, you guys just get the 3 series 3.5 ton, badged as Ram 2500) to a smaller Merc Vito which also has a 2.8 ton GVW capacity.
The 4 and 6 liter engines are basically Deutz engines with Volvo outfit and software, but that 6.1 Deutz would make some tough competition in full size pickups, its light and economical. When we checked all industrial engines available on the market, the TCD 6.1 Deutz turned out cheapest.
The Sisu engine is too large (length) and too heavy for automotive use, as it is a frameless design, with no on-road epa certification. Same goes for the Deere diesels, they are designed solely as an offroad engine. The Cummins and the FPT (Iveco) are developed with a much narrower cylinder spacing and lighter block for automotive applications. The weight difference between the Cummins block and the Sisu frameless block is 660 for the Sisu and 500 for the Cummins.
Your best bet would be the Navistar engines, they are typical on-road engines...
Anyways if Ram saw a need for a lighter industrial heavy duty diesel, they would have put the Cummins ISB4.5 in it, it would also put out around 250hp and plenty of torque.. But manufacturers dont see the need for lower hp heavy duty, proven their choice to make a lighter duty automotive style engine.