CPR had only one, six-axle Alco/MLW unit, RSD-17 8921, until the arrival of eight, MLW C630M's in 1968. CPR borrowed two, UP Alco C630's in May, 1966 for testing. They were having troubles with the new SD40's and decided to trying the competitor's product. Based on their performance many M630's and M636's would follow. 4503 was just a year old and already looking a little road weary when lashed up with an FB-2 and RS-18 ready to lead a westbound freight from St. Luc.
