I seem to be coming up short on my research... What is the difference between Phase I and Phase II? What years were these available/phased out? When did dynamic brakes become available? I want to model 1952, but there is a very limited availability of N scale GP-7s. Atlas seems to be the only manufacturer, and the undecorated locos (I want to apply my own road's paint scheme) easiest to get are Phase II w/ dynamic brakes. Would I still be within my time period w/ this engine?