Besides being quite heavy, the SD's also had offset fan and water pump pulleys for various chassis applications. With their height from oil pan to oil-bath air cleaner, width from exhaust manifold to exhaust manifold, and length from water pump pulley/cooling fan to bellhousing, it would be pretty tough to fit one in a LD truck frame.

Too, getting a radiator big enough to cool the beast on the street and getting that under the hood of a LD truck would be a chore.

Wouldn't the EPA have a brick trying to inspect one of THOSE, though?? LOL