I'm not sure if EMD 60-series locos are any more "modern" than GE Dash 8 locos. They were built in the same time period (late '80s / early '90s), and it was during that time period that GE took over as the #1 locomotive builder in the U.S.
Regarding possible weight concerns, a typical SD40-2 actually has a lower per-axle weight (total weight divided by the number of axles) than a GP40-2 or a B39/B40-8. The whole point of the Special Duty (SD) series in the beginning was that they were better suited for lighter track. Today that's not really the case anymore with the monstrous SD70ACe, but anyway that's a little history for ya'.
SD60s are a bit heavier than SD40-2s, but I think the per-axle weight is still slightly lower than a comparable-horsepower four-axle unit.
MEC407
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Pan Am Railways — Boston & Maine/Maine Central — Delaware & Hudson
Central Maine & Quebec/Montreal, Maine & Atlantic/Bangor & Aroostook
Providence & Worcester — New England — GE Locomotives