Here we have two species of the SD70 genus: the newer flared radiator CSX SD70MAC and the newer flared radiator UP SD70M...basically identical except for the UP's newer style nose...
CSXT #4830 is what I believe to be the last SD70MAC built by EMD before having to stick to the tier 2 specs...S420 leaves Selkirk with more power than usual for the Boston Line...