I believe the aluminum cover was on the 4l80 and plastic on the 4l60 transmissions, I have a couple of each on the shelve and both 4l80s have aluminum covers.Be careful which case you get. Cases out of cars have the 4 bolt plastic inspection cover while trucks have a 6 bolt aluminum one. I had that happen to me with Transmission Depot when I bought my stage 2 trans even though I told them it was for a truck.