An engine placement configuration for a heavy-duty truck includes a chassis having two spaced-apart frame rails running in a longitudinal direction of the chassis, between front and rear ends, and a front wheel assembly with an axle attached to the frame rails. An opposed-piston engine is supported on the frame rails and positioned between the front end and the axle. The opposed-piston engine includes a cylinder assembly with a longitudinal axis disposed between the frame rails and oriented vertically with respect to the longitudinal direction. Alternatively, the opposed-piston engine includes a row of cylinders disposed between the rails and running in the longitudinal direction.