As far as I know the long cooling pipes mounted alongside the radiator fans were aftercooler pipes between the air compressor and the main reservoir.  Sounds like the finned pipes on the E6s and E7s had a different purpose.  Remember, the radiators on the early Es were nothing like those on the Fs or E8s.

My understanding is the aftercooler pipes were a retrofit offered by EMD after being made standard on the F9.  So perhaps installed after 1954.  Many railroads added them to their earlier Fs.

In HO, I think Bowser sells an aftercooler pipe assembly for F units.

Scott Chatfield