Thanks Brad and Tim -
Not doubting your answers, just trying to see printed confirmation and hopefully photos of 216D and 216E.
I searched the "1954 Truck Engineering Features" book on Tim Lederman's site and the "1946 Chevrolet Truck Data Book for Chevrolet Salesmen" book on Tim Sheridan's site. Both show a pic of the air cleaner, state that it is for 3100 and other trucks, state that it is available as 1-pound and 2-pound capacity, but only give the 216 RPO number with no letter designation.
Is the "1954 Salesman Data Book" that you referenced available on line? Any idea what the 2-pound (RPO 216E) air cleaner looks like?
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1954 Truck Engineering Features>
1946 Chevrolet Truck Data Book for Chevrolet Salesmen NOTE: 340MB download!!