We tried one to baseline from a HP and an air-intake temp perspective. We built a better one by V.3 and V.4. (by my definition - torque curve)

As to the plastic over in front of the radiator, I kept mine. It actually keeps better air into the radiator. Back in the day, the 1.6 SM guys were adding the 1.8 piece IIRC to improve cooling. It might be specifically allowed in SM.