6-8265 was the first SD40. Actually the first all-new diesel introduced by Lionel since the Postwar era. I remember when they first came out, Lionel made a big deal about the fact that it was exactly as long as a Fairbanks-Morse Trainmaster (which require O gauge track.) The foreseeable problem is that the large fuel tank will hit the housing on most, if not all O27 switches. It might get through the manual version of the Marx 1590. Any other type of switch, I doubt it.