The RH/Passenger side is a great design and accomplishes 2 things: It flows better than even the 340 manifold AND it only requires one bend in the exhaust pipe approx 45 degrees. The standard straight down exit style usually has 2 bends to clear the steering. The truck manifold dumps just over the oil filter.
The LH/Driver side is a tough one. The reason it might clear in an early b body is because those cars had the engine mounted a bit further forward than the later B and other models. The exit port on the left manifold is really close to the firewall on a 67-76 A body, not sure of the fitment on other cars. If you have a 4 speed, the clutch torque shaft is in the way. Of you have a column automatic, the trans shifter linkage is in the way.