Before production began on EMD's new line of 645-engine diesels, there were various test bed diesels constructed. Commonly called SD40X diesels (and, less commonly, SDX40s) by railfans, EMD simply referred to these as SD40s, even though they differed from production SD40s in many ways - such as being built on SD35 frames, having SD45-style flared radiators (on the first four only) and having a unique AR10 alternator electrical system. On October 7, 1986, Union Pacific 3045 and 3046 were found working the hump at the railroad's Bailey Yard in North Platte, Nebraska. These were two of the six "SD40X" diesels built by EMD and later sold to the UP following their demonstration runs. Union Pacific 3045 was originally EMD 434F and UP 3046 was the former EMD 434G; each built in April 1965 and sold to the UP in February 1966. Two years and 16 days after this photo was shot, UP 3046 would be retired. Flared radiator 3045 would soldier on until October 1991.