Don. The 'B' unit in the middle is a cab less 'A' unit. Any diesel locomotive could be considered an 'A' unit, if in fact it had a cab less 'B' unit in the consist, but it was more common to say 'A' and 'B' units when EMD bulldog nosed cab units were in a consist. The EMD E 8/9 locomotives you were looking at originally had two 567 diesel engines with in the car body. If referring to a Cab unit consist, one might say they were looking at an A-B-A engine consist. U.P. did rebuild their E8/9's with a single GP38-2 645 diesel engine placed reportedly in the center of the frame. Like? Who does that? Way heavier than the 567 maybe and would need some extra support between the trucks baring the weight.... but that's another matter....