As per the the Second Diesel Spotters Guide by Jerry Pinkepank, Kalmbach Books 1973:
EMD powered articulated trainsets were the UP M-10000 (2-1934), CB&Q 9900- the original Zephyr (4-1934), BM-MEC 6000- the Flying Yankee (2-1935), QB&Q 9901- The first Twin Zephyr becoming in 1936 the Sam Houston Zephyr and CB&Q 9902- the first Twin Zephyr becoming in 1936 the CB&Q-Alton Ozark State Zephyr (both built 4-1935), and CB&Q 9903- the Mark Twain Zephyr (4-1935). Subsequent production were the various shovel nose, box cab and pre E unit locomotives hauling trains of light weight cars. CB&Q's shovel nosed power cars and locomotives 9904, 9905, 9906A-B, 9907A-B and 9908 were similar in design to the articulated trainsets but were separate locomotives not articulated with the trains.
UP M10001 and M10002 turret cab streamliners were articulated with the train while M10003-M10007 had conventional couplings. These were followed by EMD boxcabs 511-512, B&O 50 and AT&SF 1-1 which were the predecessors of the E-unit line.
Greg S