It's called a 4-53T. 4 cylinders, 53 cu. in. per cylinder, "T" is for turbocharged. These engines came with an assortment of different injector sizes, and therefore horsepower ratings, depending on the application. But standard they made about 400-450 lb. ft. @ 1800 rpm and 160-170hp @2800.
You can tell this is a 53 Series because of the way the rocker cover is bolted to the cylinder head. If it was a 71 Series the the rocker cover bolts go through the center of the cover not the outer perimeter like the 53 Series. I used to make my living working on the 6V53 in ready mix trucks in the late 1970s. I know the anatomy of this engine very well. A 71 series ( 71 cu. in. per cylinder) engine is much taller and would be difficult to fit into a pick-up truck without doing some major surgery.